The Church celebrates her belief in the Most Holy Trinity, a communion of persons of Love. This feast given to us not to celebrate the revelation of an idea and divine works in history, but to meet in a personal way the community of the Trinity.
While in Genoa for Trinity Sunday in 2008, Pope Benedict taught that
From the reality of God which he himself made known to us by revealing his “name” to us comes a certain image of man, that is, the exact concept of the person. If God is a dialogical unity, a being in relation, the highest creature made in his image and likeness reflects this constitution; thus he is called to fulfill himself in dialogue, in conversation, in encounter.
The Collect of the Mass for today is (trans. by Fr Z):
Almighty everlasting God, who granted to Your servants, in the profession of the true Faith, to recognize the glory of the eternal Trinity and to adore Its Unity in the might of majesty: we beseech You; that, in the steadfastness of that same Faith, we may always be defended from all adversities.
Perhaps you’d consider reading Joseph Ratzinger’s book, The God of Jesus Christ: Meditations on the Triune God.