Here’s a contemporary hymn to the Trinity. It was translated from the Latin by Michael Saward, and posted on Jubilate Hymns.
All Hail, Majestic Trinity!
All hail, majestic Trinity!
All hail, eternal unity!
O God the Father, God the Son,
and God the Spirit, ever one.
One living God, our hearts adore;
three Persons, now and evermore;
and in your loving mercy kind
salvation's promised hope we find.
O Trinity, O Unity,
our God, both now and ever be;
and with the songs that angels sing
we shall rejoice, all-glorious king.
~ Latin 10th Century, translated Michael Saward, after John Chambers (1805-93). Copyright © Michael Saward / Jubilate Hymns. http://www.jubilate.co.uk/ If you use this hymn in worship, be sure to report it on your CCLI license.
OLD HUNDREDTH (Praise God from whom all blessings flow)
DUKE STREET (Jesus shall reign where’er the sun)
O WALY, WALY (Tho’ I may speak with bravest fire)
or any other suitable tune in 188.8.131.52 (LM) meter.