The Second Vatican Council turned to the Trinity, not as a pious heavenly afterthought, but as the bedrock meaning of reality. Karl Rahner, sadly, amusingly but truly remarked: “We may venture to say that if the doctrine of the Trinity were to be suppressed as being false, a fairly good portion of religious literature would remain nearly unchanged in the aftermath… We may suspect that that in the catechism of mind and heart, as contrasted with the printed catechism, the representation of the Incarnation by Christians would not undergo any change at all if there were no Trinity.”
At the absolute center of the Council, in its most deliberative moment on the meaning of God and man, Gaudium et Spes #24 said: “Furthermore, the Lord Jesus, when he prays to the Father, that all may be one… as we are one’ (Jn. 17:21-22) has opened up new horizons closed to human reason by implying that there is a certain parallel between the union existing among the divine persons and the union of the sons of God in truth and love. It follows, then, that if man is the only creature on earth that God has wanted for its own sake, man can fully discover his true self only in a sincere giving of himself.”
The Novelty of the Trinity as Ground and Purification of The Enlightenment
This subjective metaphysical anthropology gives a new understanding of the human person as image and likeness of God. Up to this point, the received metaphysical anthropology has seen man as an object, i.e. an “individual substance of a rational nature” - to which “grace” is added as the category “accident.” This received understanding which seemed to be dominated by an epistemology of concepts and corresponding categories (e.g. substance and accident), tended to created dualisms like supernatural/natural, grace/nature, faith/reason, Church/State. It was ambiguous whether man had a purely natural end in his intrinsic constitution as substance, and then was elevated to a supernatural end by grace, or whether he was intrinsically capax Dei in his very constitution as man. (Note that the Catechism of the Catholic Church begins: "Chapter One; Man's Capacity for God" #27: 'The desire for God is written in the human heart, because man is created by God and for God; and God never ceases to draw man to himself"). On this reading of man as image of God, man is not understood “from below” but “from above” and hence belongs to the ontological structure of God Himself. Without detriment to the Creator/creature perspective, the operative analogy is now “person” as Prototype/image. This does not mean that the binomial "natural/supernatural" is abolished since without Christ, "nothing." But it de-reifies grace as "thing" (or "supernature") and reads it as God's Personal "Love" that dynamizes the act of self-gift of a being that is intrinsically ordered to God. On this point, Wojtyla said: “The traditional view of the human being as a person... expressed the individuality of the human being as a substantial being with a rational (spiritual) nature, rather than the uniqueness of the subjectivity essential to the human being as a person. Thus the Boethian definition mainly marked out the ‘metaphysical terrain’ – the dimension of being – in which personal human subjectivity is realized, creating, in a sense, a condition for ‘building upon’ this terrain on the basis of experience.” In a word, the tradition gave the notion of being, while the present perspective gave the descriptive phenomenology to glimpse the being of the person as subject.
From a theological perspective which takes precedence in the understanding of the human person, since God Himself did become man, and it was in view of Christ that man was created,, the Trinity is the prototype for the meaning of image, and for the meaning of divine Person and human person.
Ratzinger on Person as Relation (Not Substance)
The philosophical category, "Substance," is not an adequate category either for the meaning of person in the Trinity, in Christ, or in man. Then-Josef Ratzinger commented: “At the turn of the fifth century, Christian theology reached the point of being able to express in articulated concepts what is meant in the thesis: God is a being in three persons. IN this context, theologians argued, person must be understood as relation. According to Augustine and late patristic theology, the three persons that exist in God are in their nature relations. They are, therefore, not substances that stand next to 4each other, but they are real existing relations, and nothing besides. I believe this idea of the late patristic period is very important. In God, person means relation. Relations, being related, is not something superadded to the person, but it is the person itself. In its nature, the person exists only as relation. Put more concretely, the first person does not generate in the sense that the act of generating a Son is added to the already complete person, but the person is the deed of generating, of giving itself, or streaming itself forth. The person is identical with this act of self-donation.
“One could thus define the first person as self-donation in fruitful knowledge and love; it is not the one who gives himself, in whom the act of self-donation is found, but it is this self-donation, pure reality of act. An idea that appeared again in our century in modern physics is here anticipated: that there is pure act-being. We know that in our century the attempt has been made to reduce matter to a wave, to a pure act of streaming. What may be a questionable idea in the context of physics was asserted by theology in the fourth and fifth century about the persons in God, namely, that they are nothing but the act of relativity toward each other. In God, person is the pure relativity of being turned toward the other; it does not lie on the level of substance – the substance is one – but on the level of dialogical reality, of relativity toward the other…. Relation is here recognized as a third specific fundamental category between substance and accident, the two great categorical forms of thought in Antiquity. Again we encounter the Christian newness of the personalistic idea in al its sharpness and clarity. The contribution offered by faith to human thought becomes especially clear and palpable here. It was faith that gave birth to this idea of pure act, of pure relativity, which does not lie on the level of substance, and does not touch or divide substance; and it was faith that thereby brought the personal phenomenon into view.”
This outstanding penetration into another epistemological horizon disclosing another level of Being, the Being of the subjectivity of God, and that of the human person, is not vapid lucubration but grounded in Sacred Scripture and the Tradition of the Church. Ratzinger says: “We stand here at the point in which the speculative penetration of Scripture, the assimilation of faith by humanity’s own thought, seems to have reached its highest point; and yet we can notice with astonishment that the way back into Scripture opens precisely here. For Scripture has clearly brought out precisely this phenomenon of pure relativity as the nature of the person. The clearest case is Johannine theology. In Johannine theology we find, for example, the formula, ‘The Son cannot do anything of himself’ (5, 19). However, the same Christ who says this says, ‘I and the Father are one’ (10, 30). This means, precisely because he has nothing of himself alone, because he does not place himself as a delimited substance next to the Father, but exists in total relativity toward him, and constitutes nothing but relativity toward him that does not delimit a precinct of shat is merely and properly its own – precisely because of this they are one. This structure is in turn transferred – and here we have the transition to anthropology – to the disciples when Christ says, ‘Without me you can do nothing’ (15, 5). At the same time he prays ‘that they may be one as we are one’ (17, 11). It is thus part of the existence even of the disciples that man does not posit the reservation of what is merely and properly his own, does to strive to form the substance of the closed self, but enters into pure relativity toward the other and toward God. It is in this way that he truly comes to himself and into the fullness of his own, because he enters into unity with the one to whom he is related.
“I believe a profound illumination of God as well as man occurs here, the decisive illumination of what person must mean in terms of Scripture: not a stance that closes itself in itself, but the phenomenon of complete relativity, which is, of course, realized in its entirety only in the one who is God, but which indicates the direction of all personal being. The point is thus reached here at which … there is a transition from the doctrine of God into Christology and into anthropology.”
The Social Doctrine of the Church
This Trinitarian understanding of the human person has become the metaphysical center for the entire social doctrine of the Church and human sexuality. The anthropological formulation for the Christological and Trinitarian meaning of person has been – as we have seen – Gaudium et Spes #24. That anthropological formula: “man, the only earthly being God has made for itself, finds himself only by the sincere gift of self," issues into the two major principles of social doctrine: the principle of solidarity, and the principle of subsidiarity. “By virtue of the first, man with his brothers is obliged to contribute to the common good of society at al its levels. Hence the Church’s doctrine is opposed to all the forms of social or political individualism.
“By virtue of the second, neither the state nor any society must ever substitute itself for the initiative and responsibility of individuals and of intermediate communities at the level on which they can function, nor must they take away the room necessary for their freedom. Hence, the Church’s social doctrine is opposed to all forms of collectivism" ("Instruction on Christian Freedom and Liberation" #73).
To conclude, John Paul II said in Centesimus Annus: “This human person is the primary route that the Church must travel in fulfilling her mission… the way traced out by Christ himself, the way that leads invariably through the mystery of the Incarnation and the Redemption.
“This, and this alone, is the principle which inspires the Church’s social doctrine.”
 K. Rahner, “Il Dio Trino come fondamento originario e trascendente della storia della salvezza,” in Mysterium Salutis 3, Brescia 1969, 404 in Bruno Forte “The Trinity As History,” Alba House (1989) ftn. 1 on p. 3.
 Cf. Lk. 17, 33.
 K. Wojtyla, “Subjectivity and the Irreducible in the Human Being,” Person and Community Lang (1993) 212.
 Cf. footnote 20 to #22 of Gaudium et Spes: Cf. Rom. 5, 14; Cf. Tertullian, De carnis resurrectione, 6: “For in all the form which was moulded in the clay, Christ was in his thoughts as the man who to be:” PL 2, 282, 47, p. 33, 1. 12-13.
 J. Ratzinger, “Concerning the Notion of Person in Theology,” Communio 17 (Fall, 1990) 444-445.
 Ibid 445
 John Paul II, “Centesimus Annus” #53,