Understanding this problem requires knowing something about the sources that transmit Bach’s work. We know the St. John Passion, first of all, from a large stack of vocal and instrumental parts Bach used in his various performances. It turns out that there are four layers, each representing a performance different from the others: Versions I (1724, Bach’s first passion season in Leipzig), II (1725), III (c. 1732), and IV (c.1749, near the end of Bach’s life).

The layers of parts and the performances they represent suggest a useful working definition of a “version” of the St. John Passion: a form of the work as it was performed under Bach’s direction and as documented in a set of parts. In practice this is not so simple because what survives is not four complete sets of parts. Rather, we have the set-aside remnants of the parts for Version I (the rest are lost); the bulk of the surviving material is from version II, which is represented by an essentially complete set. Further, Bach did not make new parts for versions III or IV but instead marked up the parts from Version II. A version, then, does not necessarily correspond to a set of parts, but to the state of a set of parts at a certain moment.

Bach’s composing score is lost, but we do have a copy of it. It is partly in Bach’s hand, having been started in the late 1730s, but never completed, leaving that task to a copyist who finished it years later. The assistant made a faithful copy of his portion, but Bach, apparently not content simply to copy music he had composed almost fifteen years earlier, revised the piece as he wrote, making changes to the first ten movements. This score, then, represents a revision of the St. John Passion by the composer and is arguably yet another version of the piece. But these revisions were never heard in Bach’s time because the new readings never found their way into any of Bach’s performing parts, even those of version IV, which took place after the revisions were made.

Whether or not we regard the music in the later score as a true version we have a wealth of choices in performing the St. John Passion. The version that most modern listeners know today resembles Version I (1724). It opens with the chorus (really a choral aria) “Herr, unser Herrscher”, whose text is a poetic paraphrase of a psalm, and ends with the choral aria “Ruht wohl” and a simple chorale setting, “Ach Herr, laß dein lieb Engelein.” It includes a number of accompanied recitatives and arias among the commentary movements distributed throughout the story.

When Bach performed Version II in 1725 he replaced the poetic opening chorus with an elaborate chorale setting, “O Mensch, bewein dein Sünde groß,” the same movement that in 1736 would close the first part of the St. Matthew Passion. The closing chorale was replaced by a different one, “Christe, du Lamm Gottes,” in a setting borrowed from a cantata Bach had performed at his Leipzig audition in 1723. Bach added or replaced some of the work’s solo arias as well; altogether there are three new arias. Their texts particularly emphasize apocalyptic images and offer different perspectives of the meaning of the passion. They make it essentially a different piece, at least from a theological point of view.