underlying theme by many commentators, including Spitta and Schweitzer, who compared the unsteady theme to the vision of a sailor seeking a firm foothold on a stormy deck (). Others have interpreted the leaping theme as representing Man's parting from and return to God; or as the "great agony" () of the sixth verse; or as the anger of God appeased by the suffering of Christ (the theme followed by its inversion); or as a reference to the treading of the winepress in the passage from Isaiah 63:2–3, signifying victory over the Cross. It has similarly been suggested that the semiquaver passages are a reference to the flowing wine-blood of the communion. Visually, the quaver theme might contain a cross motif and might form an elongated Christogram on the Greek letters iota and chi in certain sections of the score. Whatever the religious significance, the musical development from the motifs is ingenious and subtle, constantly varying. The material in the semiquaver codetta (bar 6) of the fugue subject and of the countersubject (bars 7–9) is used and developed extensively throughout BWV 688, sometimes in inverted form. The theme itself is transformed in all sorts of ways, including inversion, reflection, reversal and syncopation, the variety increased by how the two upper voices combine together. Once started, the semiquaver figures form a moto perpetuo. At some points, they contain hidden versions of the quaver fugue subject; but as the work progresses, they gradually simplify to scale passages. Even the ending is unconventional, with a simulated ritardando in the last bars with the pedal silent. The chorale prelude is thus composed from a few organic motifs heard already in the first few bars. The unprecedented novelty and musical originality of such a self-generated composition might have been Bach's main intention.BWV 689 Jesus Christus, unser Heiland (Jesus Christ our Saviour) The last manualiter four-part chorale prelude, Jesus Christus, unser Heiland BWV 689 in C minor, is marked "Fuga super Jesus Christus, unser Heyland" in the 1739 print. In contrast to the previous fughettas in the previous five manualiter settings of the catechism hymns, it is a long and complex fugue of great originality, a tour de force in the use of stretti. The fugue subject is derived from the first line of the chorale. In order to facilitate the stretti which underlie the whole conception of BWV 689, Bach chose to transform the modal