"I must Create a System or be enslavd by another Mans" (Jerusalem 10:20 E153).
It's very nice when you begin to grasp the system that Blake created instead of choosing a conventional life. But the most fascinating thing is to reach some understanding of how it relates to the 'system' of the Bible.
In Joachim of Flora's Everlasting Gospel there are three stages: O.T. (the Father, who ruled by the law), N.T. (the Son where Love becomes dominant), and post-Resurrection (the Holy Spirit). Jesus told us he was leaving mortal form so that we might be led by the Holy Spirit (John 14:25-29).
Blake expressed this theory of Religion with the three zoas: Urizen with the Father, Luvah with the Son, and Los with the Holy Spirit. In his mind (at least part of the time) Urizen with the Fall became arrogant and thirsty for Power and chose to run the World; he always had his book before him, and he ruled by the book; he claimed to be God.
As The Four Zoas begins (with the Fall), Luvah is said to have stolen Urizen's horses of light (Night 1: 10.13; E305) and thereby exerted his dominance.
In Blake's poetry there's much conflict between the two zoas (psychologically thought and feeling, or reason and impulse). This conflict occurred in Blake's psyche. In the early years freedom (free love, etc.) was dominant; in the course of his life the two functions came into (or rose to) the pre-Fall balance. (You can approximately relate this to the conflict between biblical priests and prophets; it goes on throughout the Bible. Blake definitely chose prophecy, as did Jesus, love rather than law. This accounts for the high valuation he placed on forgiveness, making it virtually synonymous with the love of God and neighbor.)
Blake identified creative imagination with Los; Los was a blacksmith with a furnace. (The Bible is full of references to a furnace: Isaiah 48:10 for example; it found expression in How Firm a Foundation.
In the Bible and in Blake things are fourfold; as a myth there are four phases: Creation, the Fall, Redemption, and Apocalypse; this is the sequence of events in Blake's system and in the Bible's.