I won’t say much here—listen to the episode on Lutheran Radio UK!—except this:
The peculiar combination, usual in Bach’s time, of Luther’s original hymn with his paraphrase of the mediæval antiphon, Da pacem, Domine (Verleih uns Frieden gnädliglich) creates a beautiful effect. In the space of just over 15 minutes of music, we go from the midst of a battle and all its noise and tumult, to the heavenly peace Christ is bringing to those whom He keeps steadfast in His word—or, more literally and more properly, whom He guards us by His word.
The cantata opens with the urgent sound of the bugle call:
But it closes with the most sublimely beautiful and peaceful Amen:
That says it all!