Originally Posted by nffc

it is plainchant of course.


Also, technically not Christmas - there are seven "O Antiphons" (quite why a lot of hymn books only have five verses still escapes me) one for each day before Christmas, so the correct time for this hymn is the week before Christmas. Each of the antiphons became one of the verses of the hymns.


In some places who do choral evensong up until Christmas they flank the Magnificat with the relevant antiphon this week...