Johann Sebastian Bach is often identified as epitomizing the Baroque era and contributed significantly to the practice and theoretical development of Western music. He composed large quantities of music, including over 500 vocal compositions such as sacred and secular cantatas, motets, masses and passions. Most of Bach's cantatas date from his tenure in Leipzig. Although he is believed to have written five cantata cycles, only the first three are practically complete; the remaining two have been lost or cannot be attributed to Bach. Bach's second year in Leipzig is considered his most prolific. On the fourteenth Sunday after Trinity in 1724, Bach first presented Bwv. 78, Jesu, der du meine Seele. Using the chorale melody and hymn lyrics written by Johann Rist in 1641, Bach incorporated the entire first and twelfth stanzas into the first and seventh movements of the cantata. Furthermore, Bach paraphrased parts of Rist's poem in movements three and five; the author of the remaining text remains unknown. This paragraph is an excellent example of Bach's ability to interpret and musically enhance religious texts. The liturgical readings on this particular Sunday included the parable of Jesus and the purification of the lepers. By keeping the key of G minor, the overall atmosphere of the chorale can be perceived as unsure and uncertain, which is also supported by the text "Herr, ich glaube, hilf mir Schwachen" (Lord, I believe, help me in my weakness). As demonstrated in the previous movement, one can strive for the conviction of Christ; however, without His love, we are destined to wander aimlessly in this world. This is the weakness referred to in the text. However, as the chorale progresses towards the last two cadential points in measures 14-16, the cantata ends in the parallel key of G major. The use of the Picardy third sheds light on the final text, "in der süssen Ewigkeit" (in sweet eternity), and gives the piece a sense of resolution and hope..