The opening chorus, "" (Were God not with us at this time), is a chorale fantasia on the hymn tune. Luther's hymn is sung to the same melody as "" by Justus Jonas, which Bach had treated to a chorale cantata, . The opening chorus is an unusual composition that does not follow the scheme of instrumental ritornellos with a cantus firmus, sung line by line by the soprano in long notes. In a setting resembling a motet, the strings play colla parte with the voices, and each line of the chorale is prepared by a complex four-part counter-fugue, in which the first entrance of a theme is answered in its inversion. After preparing entrances, the chorale melody is not sung but played by the horn and the oboes in long notes, creating a five-part composition, which is unique in Bach's cantata movements. The only other piece of similar complexity, also giving the cantus firmus to the instruments, is the opening chorus of , but it is not conceived as a counter-fugue.