Instant Karma! (We All Shine On) Lyrics

Lyric discussion by Matt Parry 

Cover art for Instant Karma! (We All Shine On) lyrics by John Lennon

i thought it was a stab at the 'fast food' nation and how even the most spiritual and all powerful force of Karma is now offerd in 'Instant' form like coffee etc.. Interested in the Mc Cartney theory if anyone can elaborate