I've been using a variant of the above, same attribution, in the Oxford Book of Carols.

After the first verse, though with both first lines repeated, comes

Then why should men on earth be so sad
Since our Redeemer made us glad, (2 lines rept)
When from our sin he set us free
All for to gain our liberty.

Verse three began with "his" grace, not "thy"

Verse four ran

All out of darkness we have light
Which made the angels sing this night

Then as MMario gives it after the repeat.