Beginning on the first Sunday after Trinity 1724, Bach undertook his most ambitious systematic project: an entire annual cycle in which every cantata is built upon a single Lutheran chorale. The hymn provides not just the text but the musical DNA — its melody permeates the opening chorus, inspires the inner movements, and returns in its original harmonisation to close.

The opening choruses are the crown jewels of the cycle: massive chorale fantasias where the cantus firmus is embedded in elaborate counterpoint, with independent orchestral motifs weaving around the voices. Each is a unique architectural solution to the same problem — how to simultaneously present a familiar hymn and make it sound completely new.

The cycle was left incomplete when Bach's librettist apparently became unavailable around Easter 1725. But the approximately 40 chorale cantatas that survive form the most unified and intellectually rigorous body of work in the cantata repertoire.