Bernard Chasan wrote:

>The main outlines of the emotions and feelings expressed by Bach can be
>determined by listening to the passions and the cantatas where the text
>provides a kind of Rosetta Stone.

True enough.  But it is Bach's choral preludes for organ (all 100++ of
them) that provide the real "translation key" for his music.  Of course,
his cantatas and passions typically incorporate chorale preludes as well.
But it is the organ choral preludes that document what Albert Schweitzer
called Bach's "tone speech".  If you wish to fathom Bach's non-secular
music, start with the organ preludes.

Dave Pitzer