One of the finest books ever written about music.
BACH
"Music In The Castle of Heaven"
John Eliot Gardiner
Agreed, which is sitting on my shelf behind me next to
"Johan Sebastian Bach: Life & Work" by Martin Geck, and
"Johan Sebastian Bach" by Christoph Wolff
And on the same topic as well
"The Cello Suites: In Search of a Baroque Masterpiece" by Eric Siblin
Seems one cannot have too many books on Bach (sic)