Nobody can really explain Blake, and that's the way he wanted it. We can listen to him, try to experience with him, and draw from our own lives scraps and pictures to associate with his words and images. So do what you can with what he says here.
Four Zoas, Night 5, Verse 2 (E302)
"In Eden Females sleep the winter in soft silken veils
But Males immortal live renewd by female deaths. in soft
Delight they die & they revive in spring with music & songs
Enion said Farewell I die I hide from thy searching eyes"
Milton Percival says in Circle of Destiny on page 56:
"The form dies in order that the imaginative impulse may be released for new expression. The masculine creative world of Eden is continually sustained by feminine self-sacrifice in Beulah."Males immortal live, renewed by female deaths." The obedience of outward form to inner vision extends even to the landscape....(spaces of Beulah)...are merciful illusions, provided for the repose of the mind which has wearied of the visionary reality of Eden. They characterize the hypothetical age in which the visionary life that Blake enjoyed in ecstasy was a habitual experience. In contrast to the spaces of Beulah, which are so readily transcended, are the "Satanic spaces" of Ulro, which limit and enslave the mind that beholds them."
Damon called the Emanation the '''counterpart" of the fundamentally bisexual male.'
In Jerusalem, plate 88 (E246), we learn why the female Emanations are so essential to man.
"When in Eternity Man converses with Man they enter
Into each others Bosom (which are Universes of delight)
In mutual interchange. and first their Emanations meet
Surrounded by their Children. if they embrace & comingle
The Human Four-fold Forms mingle also in thunders of Intellect
But if the Emanations mingle not; with storms & agitations
Of earthquakes & consuming fires they roll apart in fear
For Man cannot unite with Man but by their Emanations
Which stand both Male & Female at the Gates of each Humanity"
Blake didn't depreciate the role of the female, nor did he mean what we usually mean when we use the term. The female to Blake is an image which carries many meanings but without her, man would never reach Eternity.
Albion Asleep, Jerusalem as Butterfly