The Trinity is the hardest, most mysterious of all dogmas.
There is a logic to the timing of this feast.
We focus on the Son’s Ascension to the Father, then the Holy Spirit on Pentecost, and then the Triune God the Sunday after.
God the Father created us through the Son who redeemed us and revealed us more fully to ourselves (GS 22). God the Holy Ghost sanctifies us in Christ’s Holy Church so we can enjoy communion in the Trinity in the life to come.
Here is Sunday’s Collect:
Deus Pater, qui, Verbum veritatis et Spiritum sanctificationis mittens in mundum, admirabile mysterium tuum hominibus declarasti, da nobis, in confessione verae fidei, aeternae gloriam Trinitatis agnoscere, et Unitatem adorare in potentia maiestatis.
This is glued together from new material and part of the 1962 Collect. The phrase admirabile mysterium is used to describe the Trinity in the minutes of the summit of June 411 in Carthage between Catholic and Donatist bishops. St Augustine of Hippo (d 430), whose work On the Trinity was the first great work of systematic theology in Latin, was a major player at that meeting.
SUPER LITERAL VERSION:
O God the Father, who, sending the Word of Truth and the Spirit of sanctification into the world, declared Your astonishing mystery to men, grant us, in the confession of true faith, to acknowledge the glory of the eternal Trinity, and to adore the Unity in the might of majesty.
CURRENT ICEL (2011):
God our Father, who by sending into the world the Word of truth and the Spirit of sanctification made known to the human race your wondrous mystery, grant us, we pray, that in professing the true faith, we may acknowledge the Trinity of eternal glory and adore your Unity, powerful in majesty.
Someone may have been on autopilot in adding that “we pray”. Our Latin prayers often have some phrase like “tribue, quaesumus“. This prayer doesn’t.
In this prayer I hear echoes of manifestations (epiphanies) of the Trinity in Scripture: at Jesus’ baptism by John in the Jordan when the Holy Spirit was seen as a dove and the voice of the Father was heard (cf Luke 3) and when Jesus was transfigured before the eyes of Peter, John and James (cf Matthew 17). God “made known, manifested, showed, proclaimed publicly” (declarasti, a shortening of declaravisti, from declaro) the wondrous mystery (admirabile mysterium) that He is Three in One, a Trinity of divine Persons, God the Father, God the Word of Truth, God the Spirit of sanctification, One God. It is necessary for true Christian Faith (vera fides) that we recognize (agnoscere – “announce, allow, or admit a thing to be one’s own, to acknowledge, own”) that God is Triune, One God having one divine nature in a perfect unity of three distinct Divine Persons. Man can reason toward this truth on his own, as ancient Greek Neoplatonic philosophers did. They almost got there, too. Only by the gift of Faith can we profess (confiteor) this mystery in an authentically Christian way. What reason and intellect straive after, revelation and the grace of faith must complete.
In our Collect we adore the gloria Trinitatis, the maiestas Unitatis. They have “power” (potentia). “Glory” and “majesty” in our liturgical prayers boom with the Last Things.
Maiestas is conceptually related in the writings of the Latin Fathers to gloria, Greek doxa and Hebrew kabod. Maiestas and gloria are more than simple splendor. They express our recognition of God as God. They also indicate the mighty divine characteristic which God will share with us and by which we will be transformed. The transforming glory we will receive in heaven was foreshadowed in Moses’ meetings with God, when He descended like a cloud upon the tent. After these meetings Moses’ face shone so brightly that he had to wear a veil.
Declare God’s glory in all you say and do.
Marvel, friends, at the gift that awaits us, when we die in God’s friendship. We will no longer have to grope for a glimpse God as if through some dark glass, as if through a cleft in the rock.
Face to face we shall meet MYSTERY.