REGENERATION

 When Spectres are given bodies and enter time and space, the world of generation is created for them to occupy. Before they may return to Eden they must gain experience in the physical world. The most troublesome connotation of Generation is that physical life is accompanied by physical death which is unknown in Eden and Beulah. The physical is not infinite or eternal. To facilitate the return Blake introduces regeneration - 'Resurrection from the dead' - as the return path from generation to Eden.   

The image of entering generation as passing through death's door is seen in the frontispiece of Jerusalem. Blake tells us that we do not enter alone:

Milton, Plate 32 [35], (E 132)
"For God himself enters Death's Door always with those that enter 
And lays down in the Grave with them, in Visions of Eternity
Till they awake & see Jesus & the Linen Clothes lying
That the Females had Woven for them, & the Gates of their Fathers House"  

Wikimedia
Blair's The Grave

Irene Langridge
William Blake: A Study of His Life

Death to Generation becomes birth to Eternity. The world of generation becomes the 'void outside of existence' which becomes the womb in which the spiritual body is readied for birth to Eternity. Generation has become the image of regeneration.

Jerusalem, Plate 53, (E 203)
"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"

Four Zoas, Night I, Page 3, (E 301)
"Los was the fourth immortal starry one, & in the Earth
Of a bright Universe Empery attended day & night                 
Days & nights of revolving joy, Urthona was his name
Page 4                                            
In Eden; in the Auricular Nerves of Human life
Which is the Earth of Eden, he his Emanations propagated
Fairies of Albion afterwards Gods of the Heathen, Daughter of Beulah Sing
His fall into Division & his Resurrection to Unity
His fall into the Generation of Decay & Death & his Regeneration 
     by the Resurrection from the dead"         

Milton, Plate 31 [34], (E 130)
"And all the Living Creatures of the Four Elements, wail'd
With bitter wailing: these in the aggregate are named Satan
And Rahab: they know not of Regeneration, but only of Generation
The Fairies, Nymphs, Gnomes & Genii of the Four Elements         
Unforgiving & unalterable: these cannot be Regenerated
But must be Created, for they know only of Generation
These are the Gods of the Kingdoms of the Earth: in contrarious
And cruel opposition: Element against Element, opposed in War
Not Mental, as the Wars of Eternity, but a Corporeal Strife"   

Milton, Plate 41 [48], (E 142)
"These are the destroyers of Jerusalem, these are the murderers
Of Jesus, who deny the Faith & mock at Eternal Life:
Who pretend to Poetry that they may destroy Imagination;
By imitation of Natures Images drawn from Remembrance
These are the Sexual Garments, the Abomination of Desolation
Hiding the Human lineaments as with an Ark & Curtains
Which Jesus rent: & now shall wholly purge away with Fire
Till Generation is swallowd up in Regeneration.

Then trembled the Virgin Ololon & replyd in clouds of despair

Is this our Femin[in]e Portion the Six-fold Miltonic Female      
Terribly this Portion trembles before thee O awful Man
Altho' our Human Power can sustain the severe contentions
Of Friendship, our Sexual cannot: but flies into the Ulro.
Hence arose all our terrors in Eternity! & now remembrance
Returns upon us! are we Contraries O Milton, Thou & I            
O Immortal! how were we led to War the Wars of Death
Is this the Void Outside of Existence, which if enterd into
Plate 42 [49]      
Becomes a Womb? & is this the Death Couch of Albion
Thou goest to Eternal Death & all must go with thee"    

Jerusalem, Plate 7, (E 150)
"Los answer'd...
O that the Lamb
Of God would look upon me and pity me in my fury.                
In anguish of regeneration! in terrors of self annihilation:
Pity must join together those whom wrath has torn in sunder,
And the Religion of Generation which was meant for the destruction
Of Jerusalem, become her covering, till the time of the End.
O holy Generation! [Image] of regeneration!   
O point of mutual forgiveness between Enemies!
Birthplace of the Lamb of God incomprehensible!"

Jerusalem, Plate 62, (E 213)
"Jesus replied. I am the Resurrection & the Life.
I Die & pass the limits of possibility, as it appears
To individual perception. Luvah must be Created                  
And Vala; for I cannot leave them in the gnawing Grave.
But will prepare a way for my banished-ones to return"