In this gem of a sonata, played on an original instrument, Bach hides the simplest musical theme in plain sight: one note.  Alex looks at the end of movement 3, where Bach gives a pedal point E to the viola da gamba, asking for over 30 seconds of one sustained note on this instrument.  Simple, yes, but perfectly aligned with the notes around it.  It's just another gem in the sea of jewels that is Bach's oeuvre.

Performance of this sonata by Mieneke van der Velden and Emmanuel Frankenberg for the Netherlands Bach Society