Thomas Braatz wrote (March 18, 2003):
BWV 50 - Provenance:
Not a single note of this cantata mvt. is autograph, nor do we have access to the original set of parts which Bach would have corrected. All we have are copies and copies of copies.
All of these copies have in common that they show the use of a double choir. It is noteworthy, however, that the oldest copy carries the designation “Concerto;” while the later copies include the word “Chor.” In this context, we need to be reminded by analogy of another cantata for the same feast day: “Es erhub sich ein Streit” (BWV 19) of which there are early copies from the 18th century and these also had only the 1st mvt. of the cantata with the superscript “Chor.” Had we lost the original sources from the latter cantata, we would also know this cantata [BWV 19] as having only a single, introductory mvt. for choir. Another cantata for Michaelmas, “Herr Gott, dich loben alle wir” (BWV 130) also exists only by virtue of an early copy, in which Bach’s arias and recitatives were replaced with or exchanged with other contemporary compositions. Here we can observe again the tendency to isolate the 1st mvt. from the remainder of the composition (cantata) and then separate it entirely from the remainder of its contents. Is it possible, then, that “Nun ist das Heil” with the designation “Concerto” is also simply the 1st mvt. of what once was a complete cantata?” The NBA editors think so, even though they are unable to provide hard evidence to support this contention.
There are 8 copies of BWV 50 (Mvt. 1) of which the oldest, most likely of 18th-century origin, does not even mention the name of the composer. This is copy A. Copy B is a copy of copy A; and copy C was copied from copy B; and copy D is a copy of A. Copies E and F point back to D. Copy G seems to be a copy of E or F. Copy H is a copy of the BG. This copy by the copyist Hlavacek in the 2nd half of the 19th century was probably commissioned by Johannes Brahms who performed the cantata (1st mvt.) in Vienna on December 7, 1873. The copyist had originally planned to include as additional instruments: 2 clarinets, 2 bassoons and organ which, for the most part, doubled already existing parts.
The text is taken from the Epistle for Michaelmas (Revelations 12: 10) [NLT] Then I heard a loud voice shouting across the heavens, "It has happened at last-- the salvation and power and kingdom of our God, and the authority of his Christ! For the Accuser has been thrown down to earth-- the one who accused our brothers and sisters before our God day and night.”
Spitta was the 1st to point out that Johann Christoph Bach (1642-1703) had composed a church cantata “Es erhub sich ein Streit im Himmel” in the second part of which the text “Nun ist das Heil and die Kraft” was set as a double choir composition. This certainly must have influenced J. S. Bach in setting the same text and using a double choir.
Dürr wonders whether this was an introductory or a final chorus for a cantata. He also wonders about the special circumstances that existed so that Bach would have enough singers to perform this cantata properly. Dürr mentions a conjecture by William H. Scheide that this mvt. may have originally existed as a single 5-pt. choir mvt. with the altos divided into separate parts and that the 1st performance would have taken place on Michaelmas 1723 (because of Bach’s preference at that time for the permutation fugue) and perhaps this mvt. was an inclusion/insertion into another earlier cantata (BWV Anh. 5?) This would mean that someone other than Bach undertook the expansion into a double choir. Closer examination of the double-choir version reveals an atypical chord-like ‘thickening’ of the thematic material. Reducing the piece to the 5-pt. single choir version removes nothing of its fascination.