The Recovery of the Trinity in Thought
Although belief in the Trinity is rightly considered the ‘turning point of a steadfast or declining Christian faith,’ the Trinity seems to have been banished from Christian theory and practice. ‘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 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.’
To offer the most radical absolute necessity of the revelation of the Trinity, suffice it to quote Jn. 17, 3: “This is everlasting life, that they may know thee the one true God and him whom thou hast sent, Jesus Christ.” Suffice to repeat it: one reaches everlasting life, only by knowing the Father, and we will see now that it is impossible to know the Father without knowing the Son.
Matt 11, 27: “No one knows the Son except the Father nor does anyone know the Father except the Son and him to whom the Son chooses to reveal him.” So it seems to be a closed loop. Only the Father knows the Son, and only the Son knows the Father, and him to whom the Son reveals him. So how does one get into this loop? And, of course, the reason the loop is closed is that we are dealing with the Transcendent Creator of all that is, including the human mind which/who can know the supernatural Creator only if He reveals Himself.
The ultimate point is Christ’s revelation that “no one comes to the Father except through me”
(Jn. 14, 6). Now, go again to the Samaritan woman. Christ reveals himself to her because she lowers herself by revealing “I have no husband.” She has been in adultery/fornication with 5 men and confesses to Christ at the well that she is aware of what a “husband” is and that none of the men she has been with is her husband. Christ is pleased by this answer because it reveals authenticity on her part, an openness in this dialogue with the God-man and an astounding interior conversion. His response to this humble and generous openness is to reveal – as He did with none of the Scribes and Pharisees – that He was the Messias.
And the truth is, as He revealed, “I and the Father are one” (Jn. 10, 30) Or to Philip, he who sees me, sees the Father” (Jn. 14, 9).
And this reveals what Robert Barron calls “the coinherence” of the divine Persons. It means that each is within the other in that the Father is the very action of engendering the Son, and the Son the obedience and glorification of the Father. And yet, they are each distinct persons, as Christ reveals: “The Father is greater than I” (Jn. 14, 28),
The practical takeaway of this: “That all may be one, even as thou Father, in me, and I in Thee: that they also may be one in us, that he world my believe that thou hast sent me” (Jn. 17, 20-22). That experiential testimony of the true God one and three is the oneness of Christians. We induce atheism in that we are not united, and the reality is that we are not united. East and West split in 1054, and the West split within itself as Catholic and Protestant in 1520. All further divisions in the world spring from those. The Muslims and beyond cannot “see” the true Trinitarian God because of the splinters.
Vatican II: restored the Trinity as the origin of all Christian definition. It turned to God as “I Am” – subject/personal – and pure existential relation as non-competitve Source of all being: Love and Mercy. And so the meaning of man is Trinitarian: “the only earthly being God has willed for itself, finds himself by the sincere gift of himself. Jesus Christ is not a supernatural exception to man, but his very meaning (GS #22). This Christological anthropology – i.e. becoming self by giving self away becomes the meaning of marriage, sexuality and the entire social doctrine of the Church. GS 24 bifurcates into subsidiarity and solidarity.
In sum, the Trinity has become the defining center of the world where Jesus Christ, the God-man, must have the priority in all things. See Robert Barrons’s book “The Priority of Christ,” which is a master piece in refocusing all things from this perspective.
Finally, Francis writes: “Today we can add that the Trinity is present in the temple of marital communion. Just as God dwells in the praises of his people, so he dwells deep within the marital love that gives him glory… In the end, marital spirituality is love of God. In the end, marital spirituality is a spirituality of the bond, in which divine love dwells” (Amoris Laetitia 314-315).
 Bruno Forte, “He Loved Them to the End,” St. Paul Books and Media (1993) 123, ftnt. 1, quoting Karl Rahner.