The Blessed son of God    

1) The blessed son of God only
In a crib full poor did lie
With our poor flesh and our poor blood
Was clothed that everlasting good

Ref:
Kyrieleison (Lord have mercy)

2) The Lord Christ Jesu God's son dear
Was a guest and a stranger here
Us for to bring from misery
That we might live eternally

3) All this he did for us freely
For to declare his great mercy
All Christendom be merry therefore
And give him thanks for evermore