The body of Blake's work can be thought of as his spiritual autobiography. He is speaking of nothing else than the spiritual path he traveled as he proceeded from Innocence to Experience and back to Innocence (with consciousness.) The poetry is the garment, his spiritual evolution is the body it clothes.
John Middleton Murry, William Blake, Page 378, Note for Page 204 says this:
"... in Night VII [Four Zoas] the change in Blake's attitude is fully conscious to himself: at the same moment he knows what he has been trying to do, and he knows that it has been done. Blake himself was perfectly clear about the process involved. In Milton (p. 19) he makes the distinction between the 'nether regions of the Imagination', where these critical changes come to pass in the unconsciousness, and the pure Imagination, where there is conscious knowledge of the change."
Milton, Plate 21, (E114)
"For man cannot know
What passes in his members till periods of Space & Time
Reveal the secrets of Eternity."
Murry is attempting to explain to us what is happening in Blake's psyche as well as what is happening in the poetry that Blake wrote. Murry is following the struggle within Blake that he embodied in Urizen, Luvah, Los and all the others. The writing of the poetry was part and parcel of Blake's coming to terms with his own rational, emotional, and creative selves.
As Blake resolved the internal tensions through exploring their dynamics, Murry saw a resolution first appearing in Blake's unconscious, and then the writing of it in his myth was part of the process of making it conscious. The myth developed as Blake transcended the limitations of his earlier understanding.
Murry states on page 205:
"We must remember that the change has come to pass in Orc, as it has come to pass in Urizen, as yet only in Blake's creative imagination. The poet's work is done, but it remains to be expressed. Urizen and Luvah-Orc, that is to say, are unconscious of the destiny which awaits them."
And might Blake's readers also be unconscious of their destiny when the poet's work is expressed in them.