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.
Royal Day that chasest gloom!
Day by gladness speeded!
Thou beheld'st from Mary's womb
How the King proceeded;
Whom, True man, with praise our Choir
Hails, and love, and heart's desire,
Joy and admiration;
Who, True God, enthroned in light,
Passeth wonder, passeth sight,
Passeth cogitation.
On the Virgin as He hung,
God, the world's Creator,
Like a rose from lily sprung,—
Stood astounded nature:
That a Maiden's arms enfold
Him That made the world of old,
Him That ever liveth:
That a Maiden's spotless breast
To the King Eternal rest,
Warmth and nurture giveth!
As the sunbeam through the glass
Passeth but not staineth,
Thus the Virgin, as she was,
Virgin still remaineth:
Blessed Mother, in whose womb
Lay the Light that exiles gloom,
God, the Lord of Ages;
Blessed Maid! from whom the Lord,
Her own Infant, God adored,
Hunger's pangs assuages.