Worship, not speculation
With one exception all the Church’s festivals are concerned with God’s activity in human affairs in general and in the lives of individual people in particular. Obvious examples are Christmas, Easter, Ascension Day and Pentecost; and the various days in honour of Our Lady and the Apostles and Martyrs and all the other heroic witnesses to God and his truth.
This one exception is today, Trinity Sunday, which is concerned not with what God has done and is still doing in the world, but with his Being. It is a joyful celebration of God for his own sake – because of who and what he is in himself. And it calls forth from us the adoring recognition of his perfection – loving him because he is truly lovable, praising him because he is worthy of all praise, and honouring him because honour is his rightful due.
Such is our response to the revelation of his Being, of Three Persons and One God, of one eternal Trinity in one undivided Unity. That truth has been made known to us through the life and teaching of Jesus Christ who himself summarised it before his Ascension when he commissioned his Apostles “…to make disciples of all nations, baptizing them in the name” (not names) “of the Father and of the Son and of the Holy Spirit…” (NRSV, Matthew 28:19).
We can trace the steps by which Our Lord’s teaching culminated in that sublime statement of fact; and we can see how the Early Christians confirmed it for themselves in their own experience as they were conscious of the Father and the Son and the Holy Spirit at work in their own personal lives.