This post follows posts on the first chapter of Jerusalem; To the Public and the second chapter: To the Jews.
Chapter 3 of Jerusalem is addressed to the Deists, those with a consciousness that rejects a direct and immediate connection between God and man. Sense data, processed by the rational mind, is the only admissible evidence to the Deist. The figure of Rahab is used by Blake to epitomize the Deistic perspective. The experience of the 'Spiritual Fourfold' is:
To the Vegetated Mortal Eye's perverted & single vision"
Jerusalem, PLATE 53, (E 202)
" Chap 3.
But Los, who is the Vehicular Form of strong Urthona
Wept vehemently over Albion where Thames currents spring
From the rivers of Beulah; pleasant river! soft, mild, parent stream
And the roots of Albions Tree enterd the Soul of Los
As he sat before his Furnaces clothed in sackcloth of hair
In gnawing pain dividing him from his Emanation;
Inclosing all the Children of Los time after time.
Their Giant forms condensing into Nations & Peoples & Tongues
Translucent the Furnaces, of Beryll & Emerald immortal:
And Seven-fold each within other: incomprehensible
To the Vegetated Mortal Eye's perverted & single vision
The Bellows are the Animal Lungs. the hammers, the Animal Heart
The Furnaces, the Stomach for Digestion; terrible their fury
Like seven burning heavens rang'd from South to North
Here on the banks of the Thames, Los builded Golgonooza,
Outside of the Gates of the Human Heart, beneath Beulah
In the midst of the rocks of the Altars of Albion. In fears
He builded it, in rage & in fury. It is the Spiritual Fourfold
London: continually building & continually decaying desolate!
In eternal labours: loud the Furnaces & loud the Anvils
Of Death thunder incessant around the flaming Couches of
The Twentyfour Friends of Albion and round the awful Four
For the protection of the Twelve Emanations of Albions Sons
The Mystic Union of the Emanation in the Lord; Because
Man divided from his Emanation is a dark Spectre
His Emanation is an ever-weeping melancholy Shadow
But she is made receptive of Generation thro' mercy
In the Potters Furnace, among the Funeral Urns of Beulah
From Surrey hills, thro' Italy and Greece, to Hinnoms vale."
Library of Congress
Click on LC image to enlarge
The following quotes are from Minna Doskow's William Blake's Jerusalem: structure and meaning in poetry and picture which you can read online or purchase through Better World Books.
"As Los and Albion divide,repeating the initial ongoing action of the poem, Rahab sits brooding over the description within the huge sunflower that dominates the opening plate of the chapter (pl. 53). This pictorial opening to chapter 3 parallels that of chapter 2, just as the poetical beginning does, for it also depicts a fallen female, a flower, and the sea as plate 28 does. Vala's lily of plate 28, however has been exchanged in plate 53 for Rahab's sunflower, the flower tied inexorably to time, following the sun all its life...Ironically though Rahab on her Deistic sunflower throne obscures the sun and its imaginative potential and shadows the worlds of time and space that she blankly regards. Her seated attitude with head in hands suggests Deism's philosophical abstraction and accompanying despair...Her wings , which parody the butterfly wings of Jerusalem, contain the moon, earth, and stars, but not the sun. They include the fallen elements of the universe only not the imaginative, and therefore accurately represent the Deistic natural world."
[Rahab is] "that system of mystery, self-righteousness, sin, war, generative sexuality, and moral virtue which must be overcome for the Edenic world to prevail."
"...she has acted as the sacrificial priestess in Reason's temple, as natural religion, and destructive nature within Deism."
"Left to Deism the world become pure matter under Albion's daughters and pure mathematics and empirical science under his sons."
So it is Rahab who is chosen as the image to represent the reasoning error which expresses itself in Deism. The female as materiality gains power over the male as he is cut off from a 'perception of the infinite.' Chapter 3 develops the theme of the accumulation of power in Rahab and the resulting political, social and personal ramifications. The error of Deism, produced by the loss of the imaginative connection to Eternity, fosters man's trust in reasoning along with the trust in the material or 'Natural' world of Rahab.