This hymn was used for Lauds on Trinity Sunday in the Sarum Breviary.
This is the original text of this hymn as it appears in The English Hymnal (1906) where it is listed as the Morning Office hymn for Trinity Sunday:
Father most holy, merciful and tender;
Jesus our Saviour, with the Father reigning;
Spirit of mercy, Advocate, Defender,
Light never waning;
Trinity sacred, Unity unshaken;
Deity perfect, giving and forgiving,
Light of the Angels, Life of the forsaken,
Hope of all living;
Maker of all things, all thy creatures praise thee;
Lo, all things serve thee through thy whole creation:
Hear us, Almighty, hear us as we raise thee
To the almighty triune God be glory:
Highest and greatest, help thou our endeavour,
We too would praise thee, giving honour worthy,
Now and for ever. Amen.
The original Latin text of this hymn may be found here.