This might be considered Blake's first attempt to create his own system (in order not to be "enslaved by another's"). He at least begins the myth; but through the years it will take many turns.
He began with 'a horrible event', the separation
of Urizen from Eternity, from a condition where
Earth was not; Death was not. For most of the book things are going from bad to worse.
Urizen proceeded to write the Book of Brass with the "seven deadly sins of the soul", with laws of peace, laws of love, of unity.... one command, one joy, one King, one Law.
After aeons of anguish and howlings and pains and fierce madness "the vast world of Urizen appeared".
Los (introduced here) "kept watch for the Eternals
to confine the obscure separation alone".
Pl 7: "Los wept.....Urizen was rent from his side...
and rent from Eternity." And "the Eternals said
'what is this? Death. Urizen is a clod of clay.'"
In plate 9 "Los howl'd in a dismal stupor....till the wrenching apart was healed.
But the wrenching of Urizen heal'd not."
In plate 12 Los, "The Eternal Prophet" (a blacksmith) proceeds to work on Urizen who was cursed by
In chains of the mind locked up."
Thus began the Seven Ages in which Los gave the five senses to Urizen; each one involved "a state of dismal woe". (Pl 12-13, and 15)
Los appreciated the misery and horror of Urizen's state, but nevertheless "The Eternal Prophet and Urizen clos'd"; (a pregnant sentence! Urizen had been rent from Los' side (in plate 7), but now in plate 15 they clos'd.
female pity born
Which led to Pity, which led to a globe of blood which became the first female (not very high among Blake's values, but perhaps a precursor to a better value! Look at The Four Zoas at the end of Night 7, where we learn that having finally subdued his enemy, Urizen, Los find that "his whole soul loved him he beheld him an infant")
This is a sort of turning point in the Book of Urizen.
The Eternals thought poorly of Los' division into male and female (cf Matthew 2:20-25), but Los pitied and embrac'd her. In due course Enitharmon experienced pregancy; out of that came a child whom they called Orc. And a shriek ran thro' Eternity ...at the birth of the Human shadow.
the mortal triangle
As Los grew there developed the "Chain of Jealousy", and Orc wound up chained to the top of a mountain.
(Orc represented revolution, which Blake had found to be of little or no value!). But Enitharmon "bore and enormous race'.
Urizen and his globe of fire
With the "globe of fire" lighting his journey Urizen sicken'd...to see his sons and daughters weeping, wailing. He cursed them "for he saw that no flesh nor spirit could keep his iron laws one moment.
"For he saw that life lived upon death."
Urizen wandered in sorrow and wherever he walked a strong Web formed (like a Female in embryo) "like to the human brain. And all call'd it the Net of Religion.
The Net of Religion
"Then the inhabitants of those (Urizen's) cities for "Six days they shrunk up from existence,
And on the seventh day they rested,
And they blessed the seventh day, in sick hope
And forgot their eternal life."
At the end we might say that Fuzon (Urizen's "first begotten, last born") initiated a sort of rebellion or exodus.
Feel free to ask questions.