Kathleen Raines' book Blake and Tradition gives a good source for interpretation of The Myth of the Kore (Persephone), as used by Blake. (The Greek word is Kore and the Latin word is Persephone).
We are told that Blake became interested in the Eleusinian Mysteries in about 1790. (I suppose the original and oldest story of Persephone may have been from the pen of Homer.):
Demeter (Kore) was the goddess of agriculture and marriage. Her daughter was Persephone (Prosepine). This fair maiden plucked a special flower and had the fortune to be abducted by Pluto to be queen of his Underworld. Demeter appealed to Zeus about this outrage; as a consequence Persephone was granted dual citizenship in the Underworld and the World with the freedom to move from one to the other twice a year.
The natural "species" of this myth is the natural arrangement of the yearly sequence of seasons. Persephone spent winter in Hades and the warmer months in the World. Many mythologies point toward the dual nature of man: made in the image of God, but made of clay.
Psychologically we have the angelic impulse and the devilish one. (They generally alternate more frequently than twice a year.) The literal "species" is kind of self evident: a girl raped and kidnapped-- all too common in the 21st century.
(This little lesson in the species of myths illustrates something that will become more and more obvious if you continue reading Blake: what his words mean superficially is often (or usually) far from his most significant intention.)
In the early centuries of the Christian era a close relationship existed between the "followers of Jesus" and "those of Persephone". They had much in common-- particularly salvation, which (at least ritually) was achieved in remarkably similar fashions.
In Blake Vala represents woman until Jerusalem (redeemed Vala.) Here is a simple version of Persephone's story:
In Lyca (The Little Girl Lost), we see Vala in microcosm (as Persephone). Two poems in Songs of Experience tell her story, a lovely miniature statement of the myth in all the large myths already described here described. Blake spent the next 30 years expanding, enlarging, journaling, commenting on, etc. the basic myth which we've called his 'system', namely the descent of the soul (humankind) into the world (matter) and it's return to Eternity.
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