How I loved this carol which is a song sung for the Feast of Corpus Christi, Advent and Christmas. We studied the carol in high school lit class when we tackled Chaucer that semester.
The carol is very old probably dating back to 13th-14th century England. In this video clip, folk singer Joan Baez does a worthy interpretation of this beautiful song. The most recent interpretation is by Sting in 2009 and that is cool too! You can find that in YouTube.