This text comes from Mediaeval Hymns and Sequences, edited by John Mason Neale, a historical songbook transcribed on Wikisource and reproduced from the pinned revision linked below.
Let every faithful heart rejoice,
And render thanks to God on high:
And with each power of soul and voice
Extol His praises worthily.
Into this dark world Jesus came,
And all men might His form behold;
While to the limits of the same
He passed, that we might be consoled.
To all He showed that gentle Face:
On good and bad alike it shone:
Its perfect loveliness and grace
The Lord of all concealed from none.
O love of Christ beyond all love!
O clemency beyond all thought!
O grace all praise of men above,
Whereby such gifts to men are brought!
O Blessed Face, whose praise we sing!
Here in the Way we worship Thee:
That in the Country of our King
Filled with Thy glory we may be!
To God on High be glory meet!
Equal to Thee, Eternal Son!
Equal to Thee, Blest Paraclete,
While never-ending ages run! Amen.