Why is the narrator afraid to answer the door when he hears tapping in "The Raven"?

The
narrator is alone at midnight on a bleak December night, and he has been reading quaint and
curious forgotten lore. When he suddenly hears a tapping, it naturally frightens him. He is also
somewhat unnerved by the rustling of his purple curtains. There is very little light inside his
room. Most of it is coming from the dying embers of his fireplace and from
"lamp-light" by which he has presumably been reading. What really frightens him is his
own imagination. He imagines that it might be a ghost outside, the ghost of his deceased loved
one . When he stands peering into the outer darkness without finding any human being there, he
frightens himself still further by "dreaming dreams no mortal ever dared to dream
before." These dreams, or fantasies, have to do with the possibility that Lenore, though
dead, has come back to visit him in answer to his prayers. He whispers the question,
"Lenore?" He must be feeling more and more certain that he is being visited by a
supernatural spirit. He is eventually relieved to discover that the tapping was only made by a
bird which apparently was a tame pet that had somehow gotten free and was seekiing shelter in
another human habitation.