Divine Filiation and the Trinity in Thomas Aquinas: Reassessing Rahner’s Critique

Abstract

The scholastic tradition is often criticized for starting from abstract principles or philosophical definitions. In this way, scholastic theology is frequently contrasted with post-conciliar theology, which is developed on the basis of the Paschal event, understood as the hermeneutical criterion for the whole of theology. Karl Rahner accuses Thomas Aquinas of “isolating” the Trinity from other areas of theology, such as soteriology, anthropology, moral theology, and spirituality. He also criticizes Aquinas for separating Christology from the Trinity, arguing that in the Thomistic account of the Incarnation it is not essential that the Son becomes incarnate, since any divine Person could, in principle, have done so. Rahner contends that this doctrine weakens the connection between God’s inner Trinitarian life and the missions. Consequently, our adoption as children of God would no longer be grounded in the Son’s own sonship, and what God reveals of himself in history would not truly express who he is as the Triune God. The purpose of this article is to show that such criticisms do not accurately represent Thomistic teaching and to present the doctrine of our divine filiation within a Trinitarian Christological framework. It will first examine the relationship between the immanent Trinity and the economic Trinity, then present the Thomistic doctrine of the divine missions and processions. Finally, it will address the role of the Holy Spirit and our adoptive divine filiation, all considered from a Thomistic perspective. Alongside the Summa theologiae, particular attention will be paid to Aquinas’s biblical commentaries, where he focuses on the Trinitarian economy and its implications for salvation, drawn directly from his reading of Scripture.

1. Introduction: Contemporary Theology

The scholastic tradition is often criticized for beginning from abstract principles or philosophical definitions in its attempt to explain God, Christ, and the human person. For this reason, scholastic theology is frequently contrasted with post-conciliar theology, which is developed on the basis of the Paschal event, understood as the hermeneutical criterion for the whole of theology.

Prominent contemporary theologians such as Karl Rahner accuse Thomas Aquinas of “isolating” the Holy Trinity from the other theological disciplines, such as soteriology, anthropology, moral theology and spiritual theology. According to them, the main concern of the scholastic trinitarian theology would be to show that the distinction of persons does not destroy the unity of essence and because of that the Trinity would have no relevance to the rest of theology and thus not even to the daily life of the believers. In their opinion, the treatise on the one and triune God in the first part of the Summa theologiae should be understood primarily as a metaphysical explanation of the God who creates and saves, since his nature remains fully divine even while it is possible to distinguish three distinct divine Persons within him. In this sense, the treatise on the Trinitarian God appears as a largely philosophical account, self-contained and detached from the history of salvation. It leaves aside the idea of a direct and historical self-revelation of the divine persons (Rahner 1970, p. 14; von Balthasar 1992, pp. 260–64; Moltmann 2015, pp. 352–54)1.

Karl Rahner also criticizes Aquinas for separating Christology from the Trinity, primarily because, in his opinion, according to Aquinas’s teaching on the Incarnation, any divine person could, in principle, become incarnate. Rahner argues that, if Aquinas’s view were accepted, “there would no longer be any connection between the divine missions and the intra-trinitarian life. Our sonship in grace would in fact have nothing to do with the Son’s sonship, since it might equally well be brought about without any modification by another incarnate person. That which God is for us would tell us absolutely nothing about that which he is in himself, as triune” (Rahner 1970, p. 30). Thomistic Christology is also criticized for not giving sufficient importance to the relationship between Christ and the Holy Spirit, focusing instead only on the way in which the union between Christ’s human and divine natures takes place. In sum, some argue that Thomistic theology does not fully develop a Trinitarian Christology. As a result, it can lead to an incomplete understanding of our divine sonship in Christ through the action of the Holy Spirit (Rahner 1970, p. 40)2.

These criticisms do not reflect Aquinas’s authentic doctrine. In his main systematic work, the Summa theologiae, Aquinas begins with the unity of God (qq. 2–26) and then turns to the trinitarian distinction (qq. 27–43), making clear that this distinction within God is never the result of his action in the world. In this way, God’s transcendence is safeguarded, that is, the infinite distance between Creator and creature. Yet this does not mean that such distinction has no influence on the whole of Thomistic theology. On the contrary, throughout his work, Aquinas never speaks of the divine nature or essence acting on its own, apart from personal distinction. Rather, he speaks of God acting precisely as Paternity, Filiation, and Love, and thus revealing himself to us in history. For in Thomistic thought, the divine essence never subsists as such, but always as the essence of the three divine Persons.

In the Summa theologiae, the speculative study of the Trinitarian God provides the foundation upon which all of Aquinas’s subsequent reflection is built. By contrast, in his biblical commentaries, the focus falls on the Trinitarian economy and its soteriological implications, as drawn from his direct reading of the revealed text. At the same time, these commentaries also contain the principal elements of Thomistic theology concerning divine immanence, and their closeness to the biblical sources makes it clearer that only through Sacred Scripture is it possible to affirm both the divinity and the distinction of the divine persons. In this way, in continuity with patristic theology, it becomes evident that Trinitarian faith is grounded in the history of salvation.

In recent years, there has been a growing interest in the study of Aquinas’s biblical commentaries, which for a long time had remained largely neglected (Levering et al. 2026; see also Roszak and Vijgen 2015). The Johannine and Pauline commentaries, in particular, belong to the Dominican Doctor’s mature period, as they were composed on the basis of the theology lectures he delivered toward the end of his life. In these works, Aquinas shows how the study of the immanent Trinity, developed above all in his systematic writings, illuminates the economic activity of the divine Persons.

The purpose of this article is to present the doctrine of our divine filiation within a Trinitarian Christological framework. It will first examine the relationship between the immanent Trinity and the economic Trinity, then outline the Thomistic doctrine of the divine missions. Finally, it will consider the role of the Holy Spirit and our adoptive divine filiation, always from a Thomistic perspective.

2. The Immanente Trinity and the “Dispensation” of the Eternal Plan of God

Exitus-reditus is the basic framework that Aquinas follows in his theology. It describes the circular movement whereby the created beings originate in God and return to God. It is a Neo-Platonic inheritance that Aquinas receives from Pseudo-Dionysius through St Albert the Great and that he shares with St Bonaventure. When Aquinas uses the word exitus (or egressus) to say that creatures “come forth” from God, he is clearly not talking about a Neo-Platonic, eternal and necessary emanation. As a theologian who belongs to the Judeo–Christian tradition, Aquinas conceives this exitus as a free creation that inaugurates time and the history of salvation. It is precisely because of this that, in some way, we can say that there is a lineal movement, the salvation history moving towards an end, which is inscribed within the great circular movement of exitus-reditus (Torrell 2003, pp. 55–63).

In his Commentary on the Sentences (Super Sent. I, d. 14 q. 2 a. 2), Aquinas explains that the Trinitarian processions are the ratio of both creation (exitus) and salvation (reditus)3. The word ratio is a very rich term, which can be translated in different ways such as cause, pattern, reason, motive. The eternal processions of the Son and the Holy Spirit are the reason for our return to the Father, insofar as these Persons are sent in time. The sending of the Son and the Holy Spirit allows us to know the Trinitarian intimacy, not merely in a theoretical sense, but also in an experiential and affective way; that is, to know it by becoming partakers of this divine life. The incarnation of the Word and the gifts of the Holy Spirit make present in time and for our salvation the mystery of the triune God. The missions of the divine Persons open the way for our return to the Trinity; they lead us to the heart of the Trinitarian mystery, a life of total donation.

In order to speak of the immanent Trinity, we must start from the historical revelation, that is, from those free acts through which God wished to communicate Himself, first to the people of Israel and then to each of us. When we speak of the historical revelation of the Trinity, we speak of an act flowing from divine Love, a gift from God. It is important to emphasize that the Revelation of the Persons of the Trinity responds to a free act of God, because then it is possible to affirm that, at the same time, God continues to be totally transcendent to us. We can never, with our limited capacities, understand God’s intimacy, as if it were a mathematical problem that we can solve; we can only go so far as to say that God exists as the cause of everything, but then we do not know his intimacy if He doesn’t open it to us. In other words, the revelation and the salvation that God offers us, which is identified with his intimacy, is never caused by anything other than his totally free and disinterested gift. God reveals himself because he loves us, not because of our own works or merits.

Rahner’s famous axiom that “the ‘economic’ Trinity is the ‘immanent’ Trinity and the ‘immanent’ Trinity is the ‘economic’ Trinity” (Rahner 1970, p. 22) has provided a framework for clarifying the relationship between the immanent Trinity and the dispensation of the eternal plan of God. It is often said that Rahner’s axiom is valid from an epistemological point of view, since the economic Trinity is not an arbitrary sign wholly unrelated to the divine intimacy; on the contrary, the immanent Trinity is in some way identified with the economic Trinity. At the same time, from an ontological perspective, it is not possible to speak of an absolute identity between the immanent Trinity and the economic Trinity, because the divine nature is and will always remain a mystery that exceeds us. According to Thomistic theology, the economic Trinity communicates to us the Trinitarian intimacy insofar as it allows us to share in the divine mystery; yet this never leads to a rationalism that would reduce the mystery of God to the finite limits of human comprehension. As Hans Christian Schmidbaur notes, “the economic Trinity as a revealed Trinity is, on one hand, a true and historical self-revelation of God, but, on the other hand, it stands only in an analogical relation to the immanent Trinity, because the full essence of divine nature is never expressible in a contingent world” (Schmidbaur 2009, p. 199).

In their ad extra activity, the three Persons of the Trinity act inseparably, and each effect has the whole Trinity as its source. Yet in this shared action, each divine Person works according to the distinct way of relating to the other Persons, each contributing what is proper to them (Emery 2007, pp. 161–68). To understand what distinguishes each divine Person, we must examine the sending of the Son and the Holy Spirit in time, that is, the divine missions. This expression denotes not only the procession from a principle but also its temporal realization. Thus, a mission occurs exclusively within time. In other words, “mission” encompasses an eternal procession while also introducing an additional element: its effect within time. The relationship of the divine Person to his principle, however, remains eternal.

3. Divine Missions

Based on Revelation, Theology generally distinguishes between visible and invisible missions. The missions are visible when the communication of the Person sent is accompanied by a sensible sign. The Incarnation of the Word and the descent of the Holy Spirit on the day of Pentecost are called visible missions. The mission is called invisible when it takes place without any external sign. This happens with the indwelling of the Holy Spirit in the soul of the just. In the Summa theologiae, Aquinas systematizes these concepts. Since these texts are quite well known, and in order to go deeper into this mystery, I will now analyze some lesser-known texts that show how Aquinas describes the missions of the Son and the Holy Spirit. I will especially follow his biblical commentaries on the Pauline letters and on the Gospel of John.

The first point that I would like to emphasize is that Aquinas explains the mission of the Son as being intimately united with the Person and the mission of the Holy Spirit. In the Pauline commentary, he says that the incarnation of the Son, although it is an act that belongs to the whole Trinity, in a special way is appropriated to the Holy Spirit: “Christ has been given as God’s greatest gift. Hence, his conception, although it was a work of the entire Trinity, is attributed particularly to the Holy Spirit, who is the giver and source of all graces” (Super Titum, c. 2, lect. 3, n. 68). All the historical moments of the Lord’s life are configured by the presence of the Paraclete. The Holy Spirit is the principle of all grace found in Christ, and at the same time, the Third Person is revealed by Christ (Super Ioan. c. 3, lect. 6, n. 543).

The action of the Holy Spirit in Christ’s life is especially present at the moment of his passion, death and resurrection. Aquinas relates the action of the Third Person to the cause that moved Christ to give his life on the cross in response to the Father’s love. As Aquinas says: “this was done by the Holy Spirit, through whose movement and instinct, namely, by the love of God and neighbor, he did this” (Super Heb., c. 9, lect. 3, n. 444). The cross, in a rather mysterious way, makes present in the world the eternal life of Love that exists between the Father and the Son, because the divine missions follow the ratio of the intratrinitarian processions.

Christ, by dying and rising from the dead, returns to the Father. In the Commentary on the Gospel of John, we see the pattern of exitus-reditus applied primarily to Christ: “He is leaving them, going to the Father (…). This is a mark of perfection, for a thing reaches its perfection when it returns to its source (…). He went, in his human nature, to the one with whom he was from all eternity, in his divine nature” (Super Ioan. c. 16, lect. 2, n. 2083). Death brings Christ to his perfection, that is, glorification. It does not mean absorption of human nature into divine nature, it means that after the resurrection, Christ acquires an eternal, immortal, deified life, from which we will also participate (Super Rom. c. 6, lect. 2, n. 490). As Aquinas explains in the Commentary to the Letter to the Hebrews, Christ, by rising from the dead, makes himself completely perfect and thus communicates his perfection to the members of his Body:

Then when he says, and being consummated, he mentions the fruit of his passion which is twofold. One fruit is in Christ and another in his members. In Christ the fruit was glorification; hence, he says, and being consummated, for from the instant of his conception he was perfectly consummated as to the happiness of his soul, inasmuch as it was drawn to God; but he still had a nature that could suffer, although after his passion he could not suffer. Therefore, because in this respect he was altogether perfect, he could perfect others. For it is the nature of a perfect thing to be able to engender its like.

(Super Heb., c. 5, lect. 2, n. 260)

We receive the divine perfection because Christ gives us the Holy Spirit. Aquinas notes that on the evening of the Resurrection, when the Lord appears to the Apostles and breathes the Paraclete into them, he performs a gesture similar to that described in Genesis when God breathes life into the nostrils of Adam and Eve. The human life of our first parents, deformed by sin, is now restored by Christ in the gift of the Holy Spirit (Super Ioan., c. 20, lect. 4, n. 2538).

After the Ascension, Christ withdraws from our bodily sight, but this does not mean that He abandons us, because He always remains with us through the gift of the Paraclete and His grace; in this way, He governs the world together with the Father. Aquinas emphasizes: “he mentions his leaving the world, again, I leave the world, but not ceasing to govern us by his providence, because he is always governing the world together with the Father, and he is always with the faithful by the help of his grace” (Super Ioan., c. 7, lect 16, n. 2163). In his Commentary on the Gospel of John, Aquinas raises the question: if the Son and the Holy Spirit are equal, why is it to our advantage that the Son departs so that the Holy Spirit may come? He responds: “the Son departed with respect to his bodily presence, but he came invisibly together with the Holy Spirit” (Super Ioan., c. 16, lect. 2, n. 2090). Here we see the clear connection between the visible and the invisible mission of the two divine Persons. The visible mission is ordered to the invisible mission.

In his visible mission at Pentecost, the Paraclete descends upon the disciples, because just as Christ appeared to those who remained together, so the Holy Spirit is poured into those who are united in charity: “Christ came when they were united together, and the Holy Spirit descended on them when they were united together, because Christ and the Holy Spirit are present only to those who are united in charity” (Super Ioan., c. 20, lect. 4, n. 2529). The divine missions appear not only in their individual dimension, but also in their ecclesial one.

The missions of the Son and the Holy Spirit are not to be understood as a local movement, because God does not move; nor as a change in God, because He does not change; it is the created world that changes through the divine missions. As Aquinas explains in his Commentary on the Gospel of John, “God is said to come to us not because he moves to us, but because we move to him… God is said to come to someone because he is there in a new way, in a way he had not been there before, that is, by the effect of his grace” (Super Ioan., c. 16, lect. 6, n. 1944). Because Christ is perfectly immersed in the intimate life of the Trinity, He draws us to Himself through the action of the Holy Spirit. The effect of the divine missions in us is the life of grace, through which we are introduced into the intimacy of God in a personal relationship with each of the divine Persons. As Dominic Legge explains, Aquinas’s teaching on the created effect of a divine mission may be summarized in four points: (1) it is something new in the creature; (2) through it, the divine Person sent begins to be present in the creature in a new mode; (3) it establishes a new relation between the Person sent and the creature; and (4) it is caused by all three divine Persons as a single principle of the created effect (Legge 2017, p. 23). If the sending of the divine Persons in time makes them present to us through grace, we can then ask what the divine processions involve. We will now look at this more closely.

4. Aquinas’s Relational Account of the Trinity

According to Russell Friedman, Aquinas’s approach to the Trinity entails a “relation account” (Friedman 2010, pp. 5–15). It means that Aquinas, following the patristic tradition, distinguishes two convergent and compatible analogies that allow him to offer a systematic reflection on the Trinitarian processions in relational terms. First, he draws on the so-called psychological analogy, according to which the Son is the eternal Word generated by the Father, and the Holy Spirit is the love that proceeds from the Father through the Word, just as love proceeds from knowledge in the human person. This analogy highlights the order of origin of the Persons, the substantial unity of the three of them and the immaterial nature of the divine processions. On the other hand, the analogy of relation, or analogy of perfect charity, compares the three divine Persons to three distinct human persons in a relation of communion. This analogy emphasizes the individuality of each divine Person.

As Joseph Thomas White explains, throughout the history of theology, in addition to the Thomistic tradition, it is possible to identify two other traditions that also offer a systematic reflection on the Trinitarian mystery. The first is the Franciscan tradition, whose main representatives are Bonaventure and Duns Scotus. The Franciscan approach to the Trinity tends to employ a univocal language, according to which the natural act of divine knowledge corresponds to the generation of the Son, and the natural act of divine love corresponds to the procession of the Holy Spirit. In White’s view, however, this establishes a formal distinction in God that is not valid, since it undermines divine simplicity (White 2022, pp. 375–82).

On the other hand, lies the nominalist tradition inaugurated by William of Ockham as a reaction against the earlier approach. This tradition emphasizes divine simplicity to such an extent that it denies any kind of analogy capable of explaining the subsistent relations in God. Nominalist language tends to be equivocal, and the psychological analogy is considered valid only as a metaphor. As a result, it becomes impossible to establish any real connection between the Trinitarian mystery in itself and God’s economic action. In other words, one can only affirm the possibility of formulating propositions about the Triune God that are logically or nominally consistent and that express the faith of the Church, but without offering speculative depth (White 2022, pp. 386–91).

The Thomistic position is situated between these two poles. Starting from Revelation, Aquinas is able to distinguish what is proper to the divine Persons without introducing an undue distinction within the divine nature. According to Aquinas, the economy reveals the immanent Trinity, and at the same time, our understanding of God’s action in the world is deepened when we use analogy to explore the mystery of the Trinity. Although the use of the psychological analogy in Thomistic thought is limited and apophatic, contemporary theology shows a marked rejection of it in authors such as Karl Barth, Karl Rahner, Hans Urs von Balthasar, and Jürgen Moltmann, probably because the Thomistic tradition they received does not do justice to the true thought of the Dominican Doctor (White 2022, pp. 396–408). In what follows, I will examine in greater depth the spiration of the third Person of the Trinity as the source of all graces, in order to gain a better understanding of the Thomistic position.

5. God Is Love and Communion

Aquinas explains the second divine procession by making use of both analogies: the psychological analogy and the analogy of the perfect charity. On the one hand, he explains that just as the immanent spiritual act that describes the first procession consists in generating or expressing the mental word, in the case of the second procession, the proper spiritual act is that of love, whose origin lies in the will, based on what the intellect has previously known. This analogy allows us to identify a distinct order of origin to explain the spiration of the third Person (ST q. 27, a. 3). Aquinas also affirms that the Spirit is the mutual love and the bond between the Father and the Son. That is, by giving himself to the Son, the Father is present in the Son; and by giving himself to the Father, the Son is present in the Father, with the Holy Spirit as the bond of their communion. In terms of origin, the Holy Spirit is not something intermediate between the Father and the Son, but the third Person of the Trinity (psychological analogy). From the perspective of the relationships among the divine Persons, the Holy Spirit is the fruit of love proceeding from both (analogy of the perfect charity). Aquinas presents both analogies in the following passage from the Summa theologiae:

The Holy Spirit is said to be the bond of the Father and Son, inasmuch as He is Love; because, since the Father loves Himself and the Son with one Love, and conversely, there is expressed in the Holy Spirit, as Love, the relation of the Father to the Son, and conversely, as that of the lover to the beloved. But from the fact that the Father and the Son mutually love one another, it necessarily follows that this mutual Love, the Holy Spirit, proceeds from both. As regards origin, therefore, the Holy Spirit is not the medium, but the third person in the Trinity; whereas as regards the aforesaid relation He is the bond between the two persons, as proceeding from both.

(ST I, q. 37, a. 1, ad 3)

In short, Aquinas explains the spiration of the Holy Spirit through the analogy of love proceeding from the will, while at the same time describing the Spirit’s procession as the fruit of the mutual love between the Father and the Son. In this way, the divine Persons are united not only by essence (unity) but also by relation (personal distinction), though for different reasons. In the first case, they subsist in the same nature; in the second, the Father is in the Son and the Son in the Father as the beloved is in the lover, with the bond or fruit of this union being the Holy Spirit, who moves them to self-giving. Thus, we can say that in God, intentional communion is at the same time personal communion. This shows that Thomistic doctrine is not abstract and impersonal, but quite the opposite.

This doctrine is essential for understanding the grace of adoption we receive, which can be explained only through the love that conforms the beloved to the Lover. As Aquinas writes in the Commentary on the Sentences: “the Holy Spirit, who is the love by which the Father loves the Son, is also the love by which he loves creation by imparting his own perfection upon it” (Super Sent. I, d. 14, q. 1, a. 1). The action of the Holy Spirit in the world as Love allows us to know the eternal procession of the Father and the Son, but it does not provide a full or immediate perception of the mystery revealed by faith. It means that in his Trinitarian theology, Aquinas emphasizes that the three divine Persons are the one transcendent God, whose nature is incomprehensible and whose personal communion is ineffably distinct from any human communion (White 2022, p. 411).

After outlining the main elements of Aquinas’s Trinitarian theology, I will then examine more closely the mystery of our adoptive divine filiation, taking into account the particular role of each divine Person.

6. Our Filiation to the Father in the Love of the Holy Spirit

God’s love differs radically from human love. Human love is caused by the goodness perceived in its object. In God, however, the opposite is the case: it is his love that brings goodness into being. Thus, when we say that God loves someone, we mean that he causes in the one he loves an effect that flows from divine love itself. God does not love us because he discovers goodness in us; rather, by loving us, he infuses goodness into us. This is true both at the level of creation and at the level of grace, as Aquinas explains in the Summa theologiae I–II, q. 110, a. 1.

A key biblical text in this regard is Romans 5:5: “the love of God has been poured into our hearts through the Holy Spirit who has been given to us.” In his commentary on this passage, Aquinas explains: “for the Holy Spirit, who is the love of the Father and of the Son, to be given to us is for us to be brought to participate in the love who is the Holy Spirit; and through this participation we are made lovers of God. The fact that we love him is a sign that he loves us” (Super Rom. c. 5, lect. 1, n. 392).

From this text, two points may be highlighted. First, the invisible presence of the Holy Spirit as Love implies the presence of the Father and the Son. Second, the Holy Spirit leads us to a participation in the Love that he himself is. The third Person communicates his personal characteristic to us through charity, and by this participation, we truly love God. The presence of divine Love in the soul therefore produces a new effect in us: filial love, which unites us to the Father in Christ.

The principle of the unity of God’s ad extra operations requires us to affirm that it is God—one and triune—who communicates divine filiation to us. Yet this ad extra action has an ad intra terminus within God himself: our introduction into the intimacy of the Holy Trinity. This introduction is accomplished through the Holy Spirit, since we are children of God by the sending of the Paraclete into our hearts. As Aquinas explains in his Commentary on the Epistle to the Ephesians, “adopting us into the children of God, the Holy Spirit is the Spirit of promise who also is the seal of the promise yet to be attained” (Super Eph., c. 1, lect. 5, n. 43) As Fernando Ocáriz explains, this doesn’t mean that the Holy Spirit is the efficient or the formal cause of our adoptive filiation; rather it means that we are introduced into the intratrinitarian life as children in the Son through participation in the Holy Spirit, by charity (Ocáriz 1998).

Thomas Aquinas affirms that charity “is a certain participation in the infinite charity which is the Holy Spirit” (ST II–II, q. 24, a. 7, ad 2). This participation entails not only a likeness between our charity and the third divine Person, but also a “dependence of origin that is actualized through the foundational presence of the participated Totality in the participants” (Ocáriz 1998, p. 485). The presence of the Holy Spirit within us is thus the origin of charity -or filial love- which configures us to Christ. For this reason, this participation is characterized “by a real and proper union between the human person and the Holy Spirit, which is inseparable yet distinct from the union with the Son and with the Father”4 (Ocáriz 1998, p. 485).

The Son, for his part, communicates to us a participation in his own personal characteristic: his filiation to the Father in the love of the Holy Spirit. As Aquinas explains in his Commentary on the Epistle to the Ephesians, “it must be through contact with fire that something starts to burn since nothing obtains a share in some reality except through whatever is that reality by its very nature. Hence the adoption of sons has to occur through the natural Son” (Super Eph. c. 1, lect. 1, n. 9)5. According to Aquinas, when we love someone deeply, we love not only that person but also what belongs to him. In this sense, when God loves us, he loves us in his Son, who is loved by the Father by nature. The Father loves us in Christ, and this love conforms us to his Son through adoptive filiation. Aquinas affirms: “by his nature the Son is like the Father; he is beloved before all else and essentially. Hence, he is loved by the Father in a most excellent way. We, on the other hand, are sons by adoption insofar as we are conformed to his Son; in this way we enjoy a certain participation in divine love” (Super Eph. c. 1, lect. 2, n. 16).

In other words, through the missions of the Son and the Holy Spirit, the divine Persons communicate to us what is most proper to them: their personal distinction by reason of origin from the Father. Only in this way can we be truly introduced into Trinitarian intimacy. This sheds light on the theological significance of the fact that the missions are, in a certain sense, a continuation of the Trinitarian processions. The Persons who are sent communicate to us adoptive filiation to the Father as a gift of love.

Participation in the Holy Spirit must therefore always be connected to participation in Christ. As the fruit of his infinite love, the Father sends his Son into the world. At the same time, Christ, by sending the Holy Spirit, gives us his own principle of grace. The third Person -who configured Christ’s earthly existence and enabled him to manifest historically the fullness of self-gift that characterizes the inner life of the Trinity- is the same Spirit who now acts in us when we receive grace. As Aquinas states, “through the grace of Christ, or through the Holy Spirit, we are freed” (Super Rom. c. 8, lect. 2, n. 628).

God’s action in the world never introduces a distinction within the divine intimacy. This is why calling God “Father” involves the proper name that distinguishes the first divine Person by virtue of his unique and eternal relationship with the Son in the Holy Spirit. According to Aquinas, “the fatherhood present in creatures is, as it were, nominal or vocal; but the divine fatherhood, by which the Father communicates his whole nature to the Son without any imperfection, is true paternity” (Super Eph. c. 3, lect. 4, n. 169)6. Unlike the Son and the Holy Spirit, the Father is not sent into the world, because he is “the principle not only of all creatures, but also of the divine processions” (Super Ioan., c. 1, lect. 1, n. 36). Since the divine missions extend the intratrinitarian processions, their ultimate goal is to lead us to the Father as the principle of unity and communion.

Commenting on the Pauline expression “to the Father,” Aquinas explains that it refers in a certain sense to the entire Trinity, not because the unity of essence erases the distinction of the Persons, but precisely because that unity grounds and preserves their distinction:

The way we enjoy access to the Father is through Christ since Christ works through the Holy Spirit. Now if anyone does not have the Spirit of Christ, he does not belong to him (Rom 8:9). Hence, whatever happens through the Holy Spirit also occurs through Christ. When he says to the Father, it must be understood as pertaining to the whole Trinity. For, by reason of the unity of the divine essence, the Son and the Holy Spirit are in the Father, and the Father and the Son are in the Holy Spirit. In saying to the Father he especially shows that whatever the Son possesses he has from the Father, and that he recognizes he has it from the Father.

(Super Eph., c. 2, lect. 5, n. 121)

Finally, this action of the divine Persons has not only an individual but also an ecclesial dimension. The Holy Spirit is given to the Church insofar as we receive the grace of Christ that unites us to his living Body. Thomas Aquinas speaks of the Holy Spirit as the “soul” or “heart” of this Body: “The heart has a certain hidden influence; and hence the Holy Spirit is likened to the heart, since he invisibly quickens and unifies the Church” (ST III, q. 8, a. 1, ad 3). Ecclesial communion is thus a proper work of the Holy Spirit, who preserves its unity throughout time and history, just as the mutual love of the Father and the Son constitutes the eternal unity of Trinitarian communion. In explaining what it means to be “holy and members of God’s household” (Eph 2: 19), Aquinas affirms that believers “are conformed to the whole Trinity; to the Father whom they approach, to the Son through whom, and to the Holy Spirit in whom they have access in unity” (Super Eph., c. 2, lect. 6, n. 123).

7. Conclusions

Scholastic theology is often criticized for relying on a deductive rather than a historical method to explain the mystery of Christ, the Trinity, and, consequently, the Christian life. However, this is not the case. In fact, the Thomistic tradition, unlike others, is able to articulate the relationship between the immanent and economic Trinity in a particularly compelling way. In this manner, the divine missions, as a continuation of the intratrinitarian processions, allow us to enter into the intimacy of the Trinity and relate distinctly to each divine Person.

Aquinas frames theology in terms of exitus-reditus: creation freely proceeds from God (exitus) and returns to Him (reditus) through Christ and the Spirit. The Trinitarian processions are the foundation of both creation and salvation, revealed in history through the missions of the Son and the Spirit. This revelation, a free gift of divine love, allows us to share in God’s intimacy without ever fully comprehending it.

Thomistic theology distinguishes between visible missions (such as the Incarnation and Pentecost) and invisible missions (the indwelling of the Spirit in the just). Aquinas shows that the Son’s mission is inseparably united with that of the Spirit, who shapes every moment of Christ’s life, especially his passion, death, and resurrection. Through his glorification, Christ communicates perfection to his members by giving them the Spirit, whose visible mission points to his invisible presence. The divine missions transform creatures by grace, introducing them into God’s intimacy and establishing a new relation with each divine Person.

Aquinas offers a relational account of the Trinity, using two complementary analogies: the psychological analogy, where the Son is the Word and the Spirit proceeds as love, and the analogy of perfect charity, which stresses the communion of distinct persons. This position avoids both the Franciscan tendency toward univocity (which risks undermining divine simplicity) and the nominalist rejection of analogy (which empties the Trinity of speculative depth). In Aquinas, the Spirit proceeds as love from both Father and Son, not as something intermediate but as the third divine Person, the bond of their communion. Thus, the Trinity is understood as one God in essence, yet personal communion in relation, a vision that grounds our reception of grace as participation in divine love.

Thomistic theology teaches that God’s love is not caused by our goodness; rather, His love creates goodness in us, both in creation and in grace. By the Spirit, who is Love, we are made lovers of God and introduced into the Son’s own filial relationship with the Father. Through the missions of the Son and the Spirit, we receive what is most proper to each Person—filiation and charity—which draw us into the Trinitarian life. These missions, as extensions of the divine processions, lead ultimately to the Father and have both a personal and an ecclesial dimension, since the Spirit gives life and unity to the Church as the Body of Christ.