This will come to pass by an improvement of sensual enjoyment.
But first the notion that man has a body distinct from his soul is to be expunged; this I shall do, by printing in the infernal method, by corrosives, which in Hell are salutary and medicinal, melting apparent surfaces away, and displaying the infinite which was hid.
What Blake is providing in the Marriage of Heaven and Hell is an incomplete doctrine which balances the austere religion of priest class. He is destroying the bounding line between contraries in such a manner that they collapse into each other and are consumed by their mutual antagonism. Once this revelation is fully realized, a state of all embracing confusion ascends, for if Blake is correct, any metaphor will do.
The basic point to be drawn here, is if the Bible of Hell is true, then the Bible of Heaven is false, or, that if they are both equally true, if we can wander down either and still end up in the same place, then basic doctrine of the priests who promise heaven to the passive can be folded up like linens, and set aside as a history which has already run its course.
The Book of Revelation, which is mirrored in Jerusalem, is a personal apocalypse that negates the experiences that came before. The history of Christian oppression by the Romans is mirrored by the Egyptian oppression of the Jews.
Religion is no less than the rise of the oppressed over the oppressor. The harder the oppressor pushes a group of people down, the greater the counter force the oppressor must endure. No force is exerted without a counterforce, and ultimately, the opressor's war is mere hubris and leads ultimately and invariably to their extermination.
This is an apocalypse of language, but it's also literally true in a scientific sense. The earth will be consumed in the fire of the sun when it dies, ironically.
In such an apocalypse, the symbol, which is opaque and literal, becomes transparent and infinitely variable, again the notion of Nothing as infinite potential and nothing as Reflection (in the personage of Los) become paradigmatic interpretive metaphors that help us unlock the text.
The Zero sits in the center of the number line splitting the negative from the positive values.
If the doors of perception were cleansed every thing would appear to man as it is, infinite.
For man has closed himself up, till he sees all things thro' narow chinks of his cavern.
Perspective here is like a lens refracting information toward a certain aim, a telos. In Christianity we are given a life by God which we must sacrifice in order to get to Heaven, otherwise we are doomed to burn in the eternal fires of Hell.
Blake is pointing out that Hell is only Hellish if we are tortured by our desires and ashamed of our indulgences. In fact, we damn ourselves.
From the perspective of demons, Heaven is Hell.