Okay, so Venus (a.k.a. Aphrodite, goddess of love) got mad at the most beautiful mortal woman in the world, Psyche. As it turns out, Psyche was so unbelievably hot that everybody just sort of forgot about Venus which made her (Venus) really upset.
We should also add that Venus was also, like, a total babe. How could a goddess not be? Well, poor them. Must be tough being beautiful and immortal.
In order to punish Psyche, Venus sent her son Cupid to shoot an arrow at Psyche and make her fall in love with something really ugly (like a bull).
Yes, Cupid is that little kid with the wings who shoots arrows at people to make them fall in love.
He went down to carry out his mother's sinister plan, but when he saw Psyche he was so taken with her beauty that he accidentally poked himself with the arrow and fell in love with her.
Eventually, Cupid and Psyche got a place together (Venus was not happy about this at all, so they tried to keep it a secret).
Cupid told Psyche that she couldn't ever look at him, and so all of their interactions took place in the dark. This was for Psyche's safety.
Still, Psyche got curious, and one night took an agate lamp (in some versions) and shined a light on little Cupid.
She also accidentally burned him with some oil from the lamp and it took him forever to heal (even though he's all immortal and such).
Psyche's curiosity created a whole bunch of problems, and she had to endure more punishments from Venus until finally Zeus (the boss man) intervened and made Psyche immortal so she and Cupid could be together forever.
So, by calling Helen "Psyche," the speaker essentially compares himself to a little Cupid.
This is a perfect story for comparison because it involves a beautiful woman and a younger boy.
Remember, Poe met "Helen" when he was a young boy, and she was his friend's mother.
In the second stanza, the speaker had compared Helen to "Naiads," divine creatures, but now he compares her to a mortal, Psyche.
He also, implicitly, compares himself to a god (without saying so though). Talk about a pat on his own back!
This allusion makes Helen seem a little more… real. Psyche was a mortal, after all, who only became a goddess later. But, then again, Helen still seems a little unreal because Psyche was a mortal who eventually became, you know, a goddess.
Now, before we sign off, here are some other details to consider:
The phrase "from the regions which / Are Holy Land" is a bit confusing. What Holy Land? Where is this place? Virginia?
Knowing what we know about the myth of Cupid and Psyche, the "Holy Land" probably refers to some place in the heavens where all the gods and goddesses live. The speaker implies that Helen has descended from her home in the clouds to visit the world of mortals.
In other words, this Helen-Psyche-Jane Stanard character is so unbelievably beautiful that she must have come down from the heavens.