This is a study for employing alternate picking, chordal picking and cross picking. This is really useful for creating counterpoint and playing in a much more sophisticated and harmonically rich manner. The plectrum stokes/patterns differ depending on the distances between treble and bass.
Alternate Picking works well at times but chordal picking patterns tend to work better on wider string skips. Difficult to teach really because every one will have a different perspective/leaning on it depending on their own preferred picking patterns. If you play through the Music/Tab below you will find out for yourself.
Bach Study Music/Tab:
BACH PLECTRUM CONCEPTS PART 2 VIDEO