Bach scored the cantata for four vocal soloists, a four-part choir and a Baroque chamber ensemble of up to three oboes of different kinds, strings and continuo.

[4] 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.

[2][5] 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.

Two fragments are on paper with 1723 watermarks, leading musicologists like Christoph Wolff to conclude that Bach may have written a version of Ein feste Burg ist unser Gott as part of his first cantata cycle.

Dürr suggests 1735, because in that year Bach wrote Wär Gott nicht mit uns diese Zeit, BWV 14, which had an opening chorus of a comparable structure and was also based on a hymn by Luther.

[16] The movement in D major and common time elaborates on the first stanza of the hymn "Ein feste Burg ist unser Gott" ("A Mighty Fortress Is Our God").

The Bach scholar Klaus Hofmann noted that the style relates to the "vocal polyphony of the sixteenth century", when the Luther hymn was written.

[16] The chorale also makes use of the cantus firmus, which is exclusively played in the basso continuo and oboe lines (in the movement's original form).

The second movement combines an aria and chorale: the bass sings free poetry, "Alles, was von Gott geboren" (Everything that is born of God),[18] while the oboe and soprano perform the second stanza of the hymn, "Mit unser Macht ist nichts getan" (Nothing can be done through our strength),[18] in an embellished version of the chorale melody, particularly in the oboe line.

Jones compared the "extremely florid"[19] rendition of the tune, given to the soprano in the Leipzig version, to the similar approach in the chorale played by the oboe d'amore in movement 5 of the Weimar cantata for Pentecost, Erschallet, ihr Lieder, BWV 172.

[21] The interaction illustrates the unity of Christians with Jesus that the text reflects: "dass Christi Geist mit dir sich fest verbinde" (that the spirit of Christ may be firmly united with you).

[19] The mystical element of this unity, which is also exemplified in the subsequent aria and the later duet, contrasts with the "combative" character of the outer movements, where the hymn tune prevails.

The central chorale presents the third stanza of the hymn, "Und wenn die Welt voll Teufel wär" (And if the world were full of devils).

The final movement is a four-part setting of the last stanza of the hymn, "Das Wort sie sollen lassen stahn" (That word they must allow to stand).

[16][22] Also in D major, each of the SATB lines is doubled by one or more instruments, and each part has a smaller vocal range than in other movements to make them simpler for the congregation to sing.

[15] The oldest extant manuscript of Ein feste Burg ist unser Gott is by Bach's student and son-in-law Johann Christoph Altnikol.

[27] Upon its initial publication in 1821, the cantata was positively received, as demonstrated by a laudatory 1822 article by critic Johann Friedrich Rochlitz, which praised its "profound, highly original and—one might say—unimaginable wealth of sound".

[32] The first American performance may have occurred as early as 1823 in Bethlehem, Pennsylvania; handmade copies of the parts dating to that time are held by the Moravian Archives.