Kathleen Raines' book Blake and Tradition is a good source for interpretation of the Cave of the Nymphs. A condensation of Raines' great work may be found in Blake and Antiquity, which contains considerable stuff on the Sea of Time and Space:
On the right is the cave of the nymphs who conduct innocent souls by the northern gate down into mortal life. Below the cave spread across the bottom is the Sea of Time and Space. On the upper left you see a representation of the Heavenly Realm.
Homer wrote about the Cave of the Nymphs in the 13th book of the Odyssey:
"At the head of this harbour there is a large olive tree, and at no great distance
a fine overarching cavern sacred to the nymphs who are called Naiads. There
are mixing bowls within it and wine-jars of stone, and the bees hive there.
Moreover, there are great looms of stone on which the nymphs weave their robes
of sea purple--very curious to see--and at all times there is water within it. It has
two entrances, one facing North by which mortals can go down into the cave,
while the other comes from the South and is more mysterious; mortals cannot
possibly get in by it, it is the way taken by the gods."
The Arlington Tempera contains virtually all of the items in Homer's description. Blake faithfully followed Homer in furnishing his cave. The Naiads use the mixing bowls and stone jars to prepare provisions for the descending souls. On the looms the nymphs weave bodies for them; the purple indicates these bodies contain blood.
Blake loved the looms and used them repeatedly in his prophecies; in his larger prophecies
Immediately to the left of the northern gate is the southern gate of 'return' where worthy mortals ascend into the higher realm of Eternity.
In the upper part of the picture the nymphs prepare souls for the descent into the "sea of time and space". The northern gate is filled with a stream, the current moving downward into the sea. Blake shows two souls scheduled for mortal life; each possesses a tub or pail which the nymphs prepared for them containing spiritual truth and power for the hazardous journey into the world.
But emerging from the sea we find Odysseus, the hero of Homer's Odyssey on the near shore; with his back to the shore he is putting something in the water: in accordance with Leucothea's instructions he is returning her (magic) girdle which she had lent him so he could swim ashore.In the distance Leucothea appears getting her girdle and dissolving "in a spiral of radiant cloud" (Blake and Antiquity page 6).
Once you've grasped the whole of this story you may notice how closely it parallels the primary Bible myth of Creation, Fall and eventual Redemption. It's the old, old story, and in the end there's only one story. (Jesus gave us an abbreviated version of it with The Prodigal Son.)
You may find a lot more information about the Arlington Tempera in these posts.





.jpg)

