Of the five passions mentioned by Carl Philipp Emanuel Bach and Johann Friedrich Agricola in Johann Sebastian Bach’s obituary notice of 1754 only two have survived the one based on the Gospel According to St. John and the one based on the Gospel According to St. Matthew. There was also a passion based on the Gospel According to St. Mark but only the text of that particular passion has come down to us. So what of the other two? They seem to have vanished without trace but an important point to remember is that the passions Bach presented in Leipzig weren't necessarily always composed by him. He also presented the works of other composers such Reinhard Keiser it's entirely possible that the St. Luke Passion that he presented to the congregation in 1730 and then in 1745 was another composer's work. We also know that the St. Luke Passion published in the 1895 edition of Bach's complete works and listed as BWV 246 is very unlikely to have been composed by Bach. In 1971 writing in the Bach-Jahrbuch the late Yoshitake Kobayashi wrote about an autograph copy by Bach in which he had taken the two-voice setting sung by Peter in the St. Luke passion to the words of the sixth verse of the chorale and refashioned the chorale melody to make it conform to the expanded form in use in his parish. This expansion is the basis of the expanded this chorale setting you can hear below scored for tenor and five strings, including two violas. A curiosity? Certainly, but one that will amply repay the very small amount of time it takes to listen to.