This Sunday’s feast of the Most Holy Trinity was introduced in 1334 by Pope John XXII. The Augustinian Canon Pius Parsch (d 1954), an influential scholar of the 20th-century Liturgical Movement, wrote in The Church’s Year of Grace that this feast is like “the Church’s Te Deum of gratitude over all the blessings of the Christmas and Easter seasons; for today’s mystery is a synthesis of Christmas, Epiphany, Easter, Ascension and Pentecost.”

How frequently we Catholics invoke the Trinity: constantly during Mass, making the Sign of the Cross, during our baptism and absolution from sins, beginning the Commendation of our soul on our deathbed. Clergy praise the Trinity dozens of times during the Office.

Speaking of things Augustinian, in his titanic On the Trinity, the first true systematic theological work, St Augustine of Hippo (d 430), explained how the reflection of the Triune – Three and One – God is mirrored in man himself. Augustine hypostasises – personifies – memory, intellect and will, having memory correspond to God the Father, intellect to the Son who is logos, and will to the Spirit. Coming at the mystery another way, he likens the Trinity to the mind, self-knowledge and self-love (mens, notitia sui, amor sui). He also finds the Trinity in how we perceive things. There is the external object of sight, the sense impression in the eye, and the mental attention we fix on it that unites the two. In our imaginations, too, we call a thing to mind, we have an image of a thing, and then our will directs us to the memory of it. Obvious, right?

Hear how the great Doctor concludes a prayer about the mystery (trin 15.51):

O Lord my God, my one hope, listen to me lest out of weariness I should stop wanting to seek you, but let me seek your face always, and with ardour. Do you yourself give me the strength to seek, having caused yourself to be found and having given me the hope of finding you more and more. Before you lies my strength and my weakness; preserve the one, heal the other. Before you lies my knowledge and my ignorance; where you have opened to me, receive me as I come in; where you have shut to me, open to me as I knock. Let me remember you, let me understand you, let me love you. Increase these things in me until you refashion me entirely.

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