All Bibles or sacred codes have been the cause of the following errors:—
1. That man has two real existing principles, viz., a Body and a Soul.
2. That Energy, called Evil, is alone from the Body; and that Reason, called 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 called Body is a portion of Soul discerned 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 outward circumference of Energy.
3. Energy is Eternal Delight. (2.1-2.8)

According to Blake's argument, what we call "Evil" is really just a collection of natural urges that spring from our bodies. And what we call "Good" is just a series of restrictions we place on those natural urges. If that's the case, then, it's not hard to see why he advocates for Hell and hates on angels for the rest of the book.