Blake moves from simplistic in the beginning to esoteric in the end. In the middle, the marginalia. Blake's three-way mirror of art. While many of the religious aspects seem slightly out of place today, it's Blake's reverence for Art which is the common motive and all references become symbols of the artistic. In some ways, the marginalia is Blake intoxicated on Art... brewed up in the London squalor of the day that Blake called home...

 

The Complete Poetry and Prose of William Blake (Chapter 12 - The Marginalia)