Bach's prelude to "Jesus Christus, unser Heiland, der den Tod überwand" is in style and atmosphere very reminescent to anonymus preludes from Mus Ms 30439 (a complete edition of those can be found here: http://partitura.org/index.php/choral-preludes-from-mus-ms-30439/). It starts as a solemn fugue on the first phrase of the choral melody. After one page of music the choral melody enters in the soprano voice. Since the middle voices are never far apart, it's possible to play the choral melody on a different manual with a stronger registration. In my opinion this piece lends further credibility to the supposition that the anonymous pieces from manuscript Mus Ms 30439 could be written by Johann Michael Bach as well.