I'm just listening to Angel Band, from the O Brother Where Art Thou album. I'm fascinated by this song, which is identical in structure, tone, emotion, content and even wording, though not in its extraordinary Welsh-sounding tune, to Catholic hymns of my youth.

In what context would it normally be sung?

Oh, by the way, one of the particularly nice things about the CD is that it's made up to look like an old 78: black with a wine label.