From The Marriage of Heaven and Hell, a favorite piece of mine since the 1980s. It really should be read in full to get a sense of Blake’s contrarian philosophy and complex mythos. The style is probably unlike anything ever written in the eighteenth century — poetry and prose cut together in a way that at times seems almost random (but never is) — and of course, Blake, an engraver, did the whole thing on plates that included both text and artwork (some of which look almost psychedelic today). Anyway, here’s a little taste:
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All Bibles or sacred codes have been the causes of the following Errors:
1. That Man has two real existing principles; Viz: a Body & a Soul.
2. That Energy, calld Evil, is alone from the Body, & that Reason, calld Good, is alone from the Soul.
3. That God will torment Man in Eternity for Following his Energies.
But the Following Contraries to these are True:
1. Man has no Body distinct from his Soul; for that calld Body is a portion of Soul discernd by the five Senses, the chief inlets of Soul in this age.
2. Energy is the only life, and is from the Body; and Reason is the bound or the outward circumference of Energy.
3. Energy is Eternal Delight.
*
Here’s the plate, hand-colored by Blake’s wife, Catherine:
You can get a better view, along with other pages from the book and archival notes on the piece, here:
http://www.blakearchive.org/exist/blake/archive/object.xq?objectid=mhh.h.illbk.04
Recursive 
All of Blake’s “illuminated books” were printed from plates that he engraved himself — all the more amazing when you consider that he had to engrave all that text *backwards*.