That God is Triune has been the clear teaching of the Church since the fourth century, when we began reciting the creed at Mass every week. We believe in one God, the Father almighty, maker of heaven and earth, of all things visible and invisible. We believe in one Lord, Jesus Christ, the Only-Begotten Son of God. We believe in the Holy Spirit, the Lord, the giver of life, who proceeds from the Father and the Son.

This reality is a mystery to us, which is not to say that we can know nothing of it. It is a mystery in the sense that it is always beyond us—we cannot come to the end of knowing it.

The doctrine of the Trinity is a way for us to articulate God’s inner life. To say that “Trinity” is a name for God is to say that God’s very essence and being is communion and relationship. Made in God’s image, we, too, are created for relationship. This belief sets the foundation for all we experience and believe as humans.

“God relates to us in three distinct ways of being present to our history: as Father, as Son, and as Holy Spirit; as Creator, as Redeemer, and as Sanctifier,” explains Father Richard McBrien in his encyclopedic work, Catholicism. “The triune God who created us, who sustains us, who will judge us, and who will give us eternal life is not infinitely removed from us, but is absolutely close to us, communicated in the flesh and present in our hearts, our consciousness, and our history as the source of enlightenment and community” (330).

An ancient schematic describes the relationships between the persons of the Trinity well, and it is depicted in stone on the outer wall of the chapel of Howard Hall on campus. Written in Latin, it states that the Father is not the Spirit, which is not the Son. (Pater non-est Spiritus Santus non-est Filius.) At the same time each of those persons is God (“est Deus”). Three persons, distinct from each other, each fully God, yet preserving the one-ness of God.

On this feast of the Holy Trinity, let us grow in our union with God as creator, redeemer, and sanctifier!