Sometimes the text to the chorale cantatas is only peripherally related to the readings for the day. In the case of BWV 93 not only the words but the very sound of the chorale dominates the musical discourse. The reference to Peter and the 'fishers of men" Gospel in the trope to the chorale-recitative movement #5 seems almost like an afterthought.
Bach is clearly fascinated by this tune. It appears in the cantatas more often than any other chorale. While Bach is able to find enormous variety of harmony and texture in all of his four-voice harmonizations, a look at the seven versions of this melody in the 371 chorales is instructive. Obviously these harmonizations are geared to the particular verse that he is setting, but Bach is able to manipulate any given phrase into any level of simplicity or complexity. These type of subtleties are certainly not unique but there is no doubt that these bedrock chorales such as "Wer nur den lieben Gott lässt walten" have a different response from Bach than, for instance, "Liebster Gott, wenn werd ich sterben?" the basis for the cantata BWV 8 and a relatively new tune in Bach's time; certainly not of the theological significance of a text like "Wer nur."
This minute examination of the melody produced in the opening chorus of BWV 93 an almost monomaniacal interest in the half step resulting from the cross-relation that occurs between the first and second phrases of the chorale. This little figure [G,Ab,G] so omnipresent and insistent creates an oppressive dusky atmosphere that colors the whole movement. The actual treatment of the chorale tune is unusual in that each phrase is introduced by vocal duets, then quartets of a free nature before the tune appears in long notes in the soprano. The orchestration, two oboes, strings and continuo is unusual. The oboes appear much of the time in unison. The first few bars are typical; oboes play in tight canon for a bar and a half and then revert to unison for four bars; they are independent for one bar then again play in unison. The sound of oboes in unison is a particular color not just a nicety of voice leading. It adds weight and density to the texture of the work. Everything about this movement indicates unusual care and thought even by Bach's standards.
Bach includes in this cantata two movements of a form invented by him. Individual phrases of the chorale (here sung by a solo bass) are interspersed with recitative commentary. This practice, obviously similar to the medieval technique of troping bits of chant, further expands the types of commentary possible in the chorale cantatas. The textual expansion is quite sophisticated. Sometimes it is used to modify, to explicate, or to soften the blow. Other times the inserted commentary, as is the case here, is used to intensify the ideas of the chorale. Bach here clarifies what is chant and what is recitative by using the marching eighth notes to accompany the chorale and long notes to accompany the recitative. It is completely characteristic that he uses his full chromatic arsenal to further clarify what is chorale and what is commentary; thus each section of recitative is introduced by a different kind of deceptive cadence.
A different kind of troping occurs in the following tenor aria. The first and third of the eight lines of text are directly from the chorale. The other six are poetic versions of the rest. Bach here makes no effort to differentiate musically between the two types of text. The score of the aria looks on the page very like a characteristic block-like classical slow movement, for example the Adagio from the Mozart A Major Piano Concerto K. 414 or the slow movement of Haydn's Opus 76 #1 Quartet. As one listens to the piece one hears, of course, the stylistic differences. But the block "classical hymn" manner is something that is very much available to Bach.
In the duet #4 we find a very different treatment of the chorale. The tune appears in the unison strings with the soprano, alto and continuo making an independent trio. The somewhat unspecific treatment of this particular verse is shown by Bach's willingness to arrange the movement as an organ chorale prelude (Schübler Chorale #3, BWV 647) with no sung text. It is characteristic of Bach to insert an abstract such as this at the center of an emotional and directed progression of movements such as these. The tenor chorale in the middle of Wachet auf! (BWV 140) is another example.
The second trope with recitatives is somewhat different than the first. Here the distinction between the chorale and the commentary is fuzzier. The bass lines continue to be active well into the recitative commentary. There are also two types of recitative in play here, the "dry" recitative and a kind of arioso more of the kind that we saw in Bach's earlier works. This manner is usually used at the end of a recitative and can be seen as a kind of transition to an aria. Here it is isolated in the body of the movement. We find in this movement the sole reference to Gospel reading for the day, "Hat Petrus gleich die ganze Nacht mit leerer Arbeit zugebracht und nichts gefangen." Often the relationship of the cantata text to the Gospel for the day is only tangential.
Bach often will resolve a crabbed and difficult argument with a child-like declaration of faith. He will usually choose a child's voice (soprano) and the piece will often be in a "popular" style. The final soprano aria of Cantata BWV 93 is an example; "Aus Liebe will mein Heiland sterben" from the St. Matthew Passion is the pinnacle of that manner. Here the casual, jaunty oboe line combined with the sweet piping soprano provides relief from the oppressive atmosphere of what has come before. Only one line of the chorale tune appears in the aria and it is skillfully and almost imperceptibly folded into the texture.
The final chorale harmonization is unusually simple, as if Bach's examination of this particular tune was spent.