It is interesting that the line of text that begins the Cantata BWV 79 comes from one of the most friendly and pastoral of all the Psalms, #84, for the line "God, the Lord, is sun and shield" sets off in Bach a chorus more spectacularly military than any other piece in his output. This chorus reminds one of that great Altdorfer painting of the armies of Saul. Row after row, literally thousands of soldiers all in battle formation, fighting for the forces of good. Reformation Sunday had long been the most overtly militant of Lutheran festivals and our cantata here is characteristic. But this chorus is no mere noisy battle piece. It is one of the most thrilling, stupendously energetic works he ever wrote. It begins with two high horns in fanfare over a very active tympani. Against these fanfares the strings and winds play a grand marching theme. As exciting as this, is it is only an introduction to the dazzlingly active fugue subject. This is a three voice fugue with great detail and regularity. After five statements of the theme, the horns and tympani make a grand return in the dominant to lead us into the chorus entrance. The orchestral introduction is unusually long and detailed; it is particularly distinctive to have a fugue of this complexity and detail before the entrance of the chorus. The chorus entrance itself is grand and rhetorical. It is quite some time before it enters in the fugue. The texture is further thickened by the introduction of the fugue theme passed through all of the instruments but not used fugally. By the time the chorus actually begins its fugal treatment of the theme, the tune is so familiar that Bach immediately introduces it in stretto. The stretti are both at the bar and the half bar, so that the effect is of a gradually winding coil. The pitch of excitement is unmistakeable, not only because of the stretti but the sheer bravura of dense sung counterpoint moving along at this pace. The reentrance of the thunderous horns on top of this amazing texture at is a tour de force, even for Bach. One of the most remarkable things about this chorus also is Bach's ability to mix simple block-like rhetoric with the most complex counterpoint.
After writing something this overwhelmingly grand, there is an inherent problem of what to do next. Bach follows his grandest chorus with a slim reed of a piece, a lovely little pastoral aria of simplicity and lack of pretension. Because the opening line of text is almost exactly identical to the opening of the chorus, it is clear that Bach is saying, "see, I can look at this text in a completely different way." Originally composed for alto and oboe obligato in 1725, Bach revised it in 1730 for flute obligato.
The third movement is unique in all of Bach's works. He synthesizes the fanfares from the opening chorus and makes them the accompaniment with just horns, tympani, and continuo to a harmonization of the chorale "Nun danket alle Gott." Although because they are alone and so exposed, these are probably the most demanding horn parts in all of Bach, there is a sense here is of a thinning out, and clarity. The fugue theme, which was the animating force in the first movement, is completely absent. The effect of this movement is of thanksgiving after a battle.
The following secco recitative for bass and duet for bass and soprano, with all of the violins obbligato, is unusual. The two singers in the duet almost never sing contrapuntally. There is a sense of two small people against the forces of evil. The obbligato for the violins is slim, almost sketchy in sound. While there is something distinctive and appealing about the piece, there is also a sense that it doesn't occupy enough space after the two monumental chorus pieces. The horns and tympani return in the simple chorale, a setting of "Wach auf mein Herz und singe."