Canonic Variations on "Vom Himmel hoch da komm' ich her"
The Canonic Variations are based on the Christmas Hymn "Von Himmel hoch, da komm ich her". The words and melody were composed in 1539 by Martin Luther. Bach had used the chorale (hymn tune) before.  It comes in his Christmas Oratorio, in his Magnificat, and in several organ preludes including the short one from the Orgelbüchlein (Little Organ Book) which can be heard in Britain and other countries on radio and television each Christmas Eve at the end of the world-famous carol service from King’s College, Cambridge.