Ein feste Burg ist unser Gott BWV 80 (Carus 31.080/00) is one of Johann Sebastian Bach’s most frequently-performed cantatas. But the well-known form of the work, with its great opening chorale chorus, represents the final stage of a multi-layered version history, beginning with the cantata Alles, was von Gott geboren BWV 80a, probably composed for Oculi Sunday (the third Sunday in Lent) 1716. As no cantatas were performed during Passiontide in Leipzig, if Bach wanted to re-use the cantata he had...