Ein feste Burg ist unser Gott
Bach wrote the cantata in Leipzig for Reformation Day, celebrated annually on 31 October. In composing this work, Bach reused an earlier cantata, "Alles, was von Gott geboren", BWV 80a, which he wrote in Weimar for the third Sunday in Lent and based on a text published in 1715 by Salomon Franck. This work, on which the Leipzig versions were based, was one of a few in which Bach quoted the same hymn twice, in a closing chorale and in an instrumental cantus firmus in the opening movement. In BWV 80a, he used the second stanza of Luther's hymn "Ein feste Burg ist unser Gott" ("A Mighty Fortress Is Our God"), which is "Mit unser Macht ist nichts getan" (With our might nothing is done), for the closing chorale. Bach could not use the earlier work at its intended time in Leipzig, because cantata music was prohibited there during Lent.