In modern terms, we have the notion of the fractal which is an example of an infinitely complex geometric object. This same notion would have been understood in Blake's time by "seeing the microcosm in the macrocosm", that is to say, the search for a scale invariant rule set which works all the time. When we think of Bohr's planetary vision of the atom, we are left with the sense that this notion is scientifically mistaken.
Then I asked: 'does a firm perswasion that a thing is so, make it so?'
He replied: 'All poets believe that it does, & in ages of imagination this firm perswasion removed mountains; but many are not capable of a firm perswasion of any thing.'
The firm persuasion is no less than Faith itself. We can bend reality to our looking glass if we are firm enough, but we must be certain that the reality we invest our faith in is worth the investment. And we must understand that one man's heaven is another man's hell. Here faith is a matter of imagination which demands we ontologically commit to something that is in essence a lie we tell ourselves to come to some sort peace.
Then Ezekiel said. 'The philosophy of the east taught the first principles of human perception: some nations held one principle for the origin & some another; we of Israel taught that the Poetic Genius (as you now call it) was the first principle and all the others merely derivative, which was the cause of our despising the Priests & Philosophers of other countries, and prophecying that all Gods would at last be proved to originate in ours & to be the tributaries of the Poetic Genius; it was this that our great poet King David desired so fervently & invokes so pathetic'ly, saying by this he conquers enemies & governs kingdoms; and we so loved our God. that we cursed in his name all the deities of surrounding nations, and asserted that they had rebelled; from these opinions the vulgar came to think that all nations would at last be subject to the jews.'
'This' said he, 'like all firm perswasions, is come to pass; for all nations believe the jews' code and worship the jews' god, and what greater subjection can be?'
Taking Blake's argument literally, the Jews, Christians, and Muslims are worshipers of their own imagination, insisting on the literality of their vision to the mutual exclusion of all others. It is the stupidity of the mutex (programming lingo for mutual exclusion) that Blake is trying to free us from so that we may mutually see each other as brothers. Of course, we all share the tradition of Cain and Abel, so brotherhood is not necessarily a good thing. But Blake's argument is for a form of "good narcissism" which allows us to recognize what is common to us all, namely, that Genius (with a big G) is the gift of God to all nations, not one over the other.
The second point to be made here is that the religious tradition of the East teaches us the principles of perception. Namely, to see the surface clearly is the work of sages. And this is echoed in the Piper who wants to "stain the water clear".
So if we take Blake at his word, or see what he is doing as literally true, we can only conclude that Blake, at this point in his career, is an atheist using religious expression to destroy religion.