Blake called it Natural Religion or Druidism. He meant by Natural Religion the worship of the principle of fallen life; those most conformed and faithful to it become the rulers of this world. Natural Religion involves choosing to remain at the level of the material, which Blake called vegetative life.
The believer in Natural Religion closes his mind to the reality of spiritual development; he turns his back upon the Spirit. Unable to endure the tension of struggling and waiting for spiritual evolution he erects a golden calf. He either acquiesces in or actively contributes to the brutishness and horror of a life that "lives upon death".
The Bible and Blake's poetry alike are filled with gory images of this ultimate horror, which comes from identifying life with the merely natural. T.S.Eliot said in The Sacred Wood that Blake's poetry is unpleasant, as all great poetry is unpleasant. It is "unpleasant" basically because Blake, like the Bible, insists on calling a spade a spade. Nowhere is Blake closer to the Bible than in his constant reiteration of the ultimate horror of unredeemed life, celebrated in page after page of minute particulars.
Blake and the Bible both insistently remind us that Nature is fallen , and that one flows with this fallen Nature to one's destruction. Abraham and Moses knew a higher God: he was above Nature; he was Spirit. He called men to rise above the natural and to become sons of a God opposed to everything Astarte stood for, to live by the laws, not of earth, but of heaven.
The children of Abraham tried to put this God first, but rarely with notable success. Instead at every opportunity they turned away from Jehovah "under every green tree", back to Nature. This inevitably led back to Captivity in the iron furnaces of Egypt/Babylon/Rome, etc. The biblical cycle discussed above thus relates to the alternating dominance of Jehovah and Astarte. Blake's myth recreates this biblical story, but with one vital difference.
Vala and her fellow females--Tirzah, Rahab, the Daughters of Albion--represent the various forms of Astarte, the Earth Goddess. Urizen represents Jehovah, the Sky God. But in 'The Four Zoas' both are fallen. Blake claims that the Hebrew consciousness of God is flawed at best. Secular materialists had reached this conclusion long before, but it was a startling and revolutionary idea for a man like Blake, embedded in the biblical faith and firmly attached to the life of the Spirit.
Blake had made as serious a commitment to the Eternal as anyone could, and now at the mid point of his life he saw an Eternal without a God worthy of worship. It was a dark night of the soul indeed!
This honest and painful confrontation with what was for Blake an existential reality has made him into the pariah of the orthodox. The black book has no place for any criticism of the Hebrew consciousness of God; he is perfect from first to last, and everything the Bible says about him is perfect (inerrant!) as well. The superstitious awe which has been called bibliolatry forbids any questions of Abraham's God or Moses' God.
Although when we read without blinders, we can see their consciousness of God changing before our eyes. Note Abraham bargaining with God for the survival of his nephew in Sodom and Moses simply defying God if he refuses to forgive the worshippers of the golden calf. In the spirit of these two revealing passages Blake in his own recreation of the biblical story dramatically portrayed an evolving God consciousness, which the black book simply cannot permit. It was Blake's willingness to let the old die that made him notably ready for the new birth. The dark night of the soul had intensified until it became the Sickness unto Death."