When I first began to study the cantatas, now over twenty years ago, I was especially struck by how often Bach employed modest three-part structure, typically, voice, solo instrument, and continuo, and how much he did with it. In addition to the text, almost invariably important, and the meticulous attention to enunciation of it, the selection of voice type and of instrument (either in support or in contrast) produced a sound of special quality, to which the continuo, and the instruments included in it, contributed the critical bass line of the movement in question. Sometimes, Bach even dispensed with the solo instrument, to use a two-part structure, as he does in this cantata, in its fifth movement; where, in having the bassoon, and its distinctive timbre, double the keyboard continuo, a three-part motion is partially evinced even in the two-part structure. Sometimes interpreters will assign the continuo part to the strings (as in the clip included below), which I think is a mistake, as it obscures the form Bach ascribed to the aria, and makes the aria a touch fulsome rather than inescapably direct, individuated, and plain in its presentation of belief to the congregation, and how it shows of a path, a way, to know divinity and oneself. Moreover, it reduces the sensation of magnificence of effect of the richly scored chorale that concludes the work. I call to You, Lord Jesus Christ, / I beg You, hear my cries, / grant me mercy at this time, / do not let me despair.
The bass recitative in cantata 185, wherein Bach returns more directly to Biblical teachings, refers explicitly to the parable of the mote and the beam (i.e., a large piece of wood, not a stream of light), upon which the bass aria then comments. Das ist der Christen Kunst: / Nur Gott und sich erkennen (This is the Christian goal: to know God and oneself), and not to judge nor deprecate.