If you want to appreciate the symbolic density of Blake, this dictionary is extremely useful. ( )

An invaluable guide for reading William Blake.

"The MUNDANE EGG is this three-dimensional world of time and space, in which fallen Man incubates until he hatches and re-enters Eternity. Man's consciousness has shrunk: the greater part of the four Zoas remain outside his ken. The Egg stretches 'from Zenith to Nadir in midst of Chaos' (Milton 34:34). The lower half of the Egg (mostly in Urizon) is the Limit of Opacity, or Satan, whose flames ascend beyond his sphere towards the upper half of the Egg (mostly in Urthona), which is the Limit of Contraction, or Adam (Milton 19:15; Jerusalem 59:10).
"Los creates the Egg as a protection. 'We form the Mundane Egg, that [for] Spectres [the unborn] coming by fury or amity, all is the same, & every one remains in his own energy' (Milton 25:42)." (287-288)

"VISION is the perception of the human in all things. All nature is a projection of ourselves. 'As a man is, So he Sees.' Each person sees the universe in his own way.... No two painters could possibly paint the same landscape identically. 'All that we See is Vision' (Laoc, K 776). However, it is seen 'not with but through the eye.' The psychological term is empathy; it is the direct contrary of Ruskin's unfortunate theory of the Pathetic Fallacy.
"Blake's visions were not supernatural: they were intensifications of normal experience....
"Blake distinguished four degrees of Vision.... Single vision is not properly 'vision' at all: it is seeing with the physical eye only the facts before it.... Twofold vision is seeing 'through' the eye: it is the perception of the human values in all things.... Threefold vision... is the creative state, where thought appears in emotional form. Fourfold vision ... is the mystical ecstasy..." (436-437)