... with a little help from his Dad. This is, of course, an arrangement of the Orgelbüchlein choral BWV 639. There are three sources for this chorale, two of which attribute it to CPE Bach rather than the more ambiguous Bach.
When I first started working on the piece, I assumed that CPE had merely added an introduction and a few interludes to the original and kept everything else unchanged. I then found that he had changed some of the ornamentation in the chorale melody which seemed understandable. I also found a few significant changes in the left hand which, to my ear, were not as successful as the original. I was tempted to change them back, but as all three MS sources agree exactly, I did not, figuring that he wrote what he meant and he meant what he wrote (to loosely borrow a quote). It is interesting to speculate about what CPE heard in the original work that prompted him to write this arrangement.