literary analysis on "Alone" by Edgar Allan Poe

I am writing a Lirterary (sorry about the spelling) Analysis on the above poem, i have a basic idea but i am still confused from:
"From the thunder and the storm,
And the cloud that took the form
(When the rest of Heaven was blue)
Of a demon in my view"
those lines i am having a hard time attempting to figure out what he meant. Any help would be nice! thanks!