Found the Hymn I was thinking of. Amazing how much theology is concisely presented in its verses:
Sing Praise to Our Creator (O Most Holy Trinity)
Sing praise to our Creator,
O you of Adam’s race —
God’s children by adoption,
baptized into his grace.
Refrain:
O most holy Trinity,
Undivided Unity;
Holy God, mighty God,
God immortal, be adored.
To Jesus Christ give glory,
God’s co-eternal Son;
as members of his Body
we live in him as one. (Refrain)
And praise the Holy Spirit
poured forth upon the earth;
who sanctifies and guides us,
made strong in our rebirth. (Refrain)
We sang that at a Daily Mass before Trinity Sunday.