The following is taken from Pope Benedict's address on this Feast of the Holy Trinity:
Today we contemplate the Most Holy Trinity as it was made know to us by Jesus. He revealed to us that God is love “not in the unity of a single person, but in the Trinity of a single substance” (Preface): the Trinity is Creator and merciful Father; Only Begotten Son, eternal Wisdom incarnate, dead and risen for us; it is finally the Holy Spirit, who moves everything, cosmos and history, toward the final recapitulation. Three Persons who are one God because the Father is love, the Son is love, the Spirit is love. God is love and only love, most pure, infinite and eternal love. The Trinity does not live in a splendid solitude, but is rather inexhaustible font of life that unceasingly gives itself and communicates itself. We can in some way intuit this, whether we observe the macro-universe: our earth, the planets, the stars, the galaxies; or the micro-universe: cells, atoms, elementary particles. The “name” of the Most Holy Trinity is in a certain way impressed upon everything that exists, because everything that exists, down to the least particle, is a being in relation, and thus God-relation shines forth, ultimately creative Love shines forth. All comes from love, tends toward love, and is moved by love, naturally, according to different grades of consciousness and freedom. “O Lord, our Lord, / how wondrous is your name over all the earth!” (Psalm 8:2) -- the Psalmist exclaims. In speaking of the “name” the Bible indicates God himself, his truest identity; an identity that shines forth in the whole of creation, where every being, by the very fact of existing and by the “fabric” of which it is made, refers to a transcendent Principle, to eternal and infinite Life that gives itself, in a word: to Love. “In him,” St. Paul says, on the Areopagus in Athens, “we live and move and have our being” (Acts 17:28). The strongest proof that we are made in the image of the Trinity is this: only love makes us happy, because we live in relation, and we live to love and be loved. Using an analogy suggested by biology, we could say the human “genome” is profoundly imprinted with the Trinity, of God-Love.