Following Mass this afternoon was a hearty serving of lessons and carols. I think there is possibly an older name for the custom, and I am sorry, on more than one level, that I was scarcely at my best and brightest, leaving the explanation we got to trickle through my head, like water through a sieve. But if I can't tell you where the custom arose, I can, at least, report that it's quite a lovely one. The lessons were Bible readings, mostly Old Testament prophecies with a music of their own (doubly so the quote from Isaiah about "Every valley shall be exaulted," which one instinctively expected to sprout wings of Handel) and the carols of the rarer Advent variety. I was startled and delighted to hear a musical setting of "Adam Lay Ybounden," the medieval lyric that is, purposely or not, a spoken siubhal variation on St. Augustine's felix culpa.
The wise of the world (as represented by Wikipedia) believe the poem originally existed as a song, though none of the original tune has survived. Below is a modern setting similar to the one I heard this afternoon (and yes, though much of the pronunciation was updated, as far as I could tell, our choir, also, used the wonderful phrase "we moun singen").