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 the faithful raise the lay
To the new-born King to-day:
That the Light of Light would come
From the Virgin's holy womb:
Purging Adam's guilt away,
Shedding joy and scattering gloom.
Long had darkness reigned around:
Light and freedom none were found,
Hope of exit none in ken
For the fallen tribes of men,
Whom the Prince of this world bound
Fast within his doleful den.
From the dungeon and the cave
Had the Law no power to save:
While the wounded traveller lay
Breathing of his soul away,
There the Priest no aidance gave,
So the Levite, passing by,
On him cast an idle eye:
For the Law, that sin displayed,
Showed its stain, but gave no aid,
Till to succour her drew nigh,
Grace, with mightier powers arrayed.
Prophet's staff was sent before,
But the child was ne'er the more
Raised to life, until He came
Who had sent afore the same:
God and man, whom Mary bore,
Taking of an infant frame.