Blake was not a Gnostic! But he freely used gnostic ideas
like he freely used biblical ideas, platonic and neo-platonic
ideas and many other ideologies. Here's an extract from a
google book (click on the image to blow it up):
But there is certainly a relationship. Blake's myth involved
four levels: Eternity, Beulah, Ulro, generation/regeneration.
"In the Gnostic view, Hylics, also called Somatics (from Gk το σώμα, soma the body or of the body), were the lowest order of the three types of human. The other two were the Psychics and the Pneumatics (from Gk το πνεύμα, spirit, breath). So humanity comprised matter-bound beings, matter-dwelling spirits and the matter-free or immaterial, souls." in the Free Dictionary.
"When the Morning Stars Sang Together" Illustrations to the Book of Job (Butts Set) Click on picture for details.
The somatic (or hylic) level corresponds roughly to Paul's
appellation or his 'slackers': "their god is their stomach"
(Philippians 3:19). For Blake they dwell in Ulro.
The psychic dwell in matter, but that's not the only thing on their
minds. For Blake they are the created, the redeemed, those
struggling for a spiritual dimension under the care of Los.
They may eventually rise to Beulah.
The Pneumatic is matter free. We're told that in the gospel of
Judas Jesus was pneumatic and his disciples were somatic.
Jesus, the Universal Man, came down from Eternity for our
sakes. Blake calls his universal man Albion. He came down to
Beulah, passed through the two lower types, and finally at the
end of Jerusalem became synonymous with Jesus.
Blake perceived that as the eventual fate of all of us.
So did Blake get his levels of humanity from this gnostic
system? Who can tell? He may have developed his system
from any number of sources. He was a voracious reader. A
good way to learn about Blake's sources is by reading the
Perennial Philosphy, which contains thousands of sources of
divine meaning throughout Western civilization.