At first the narrator thinks it is a visitor rapping at his chamber door. Then when he opens the door and looks outside he feels frightened because he suspects that it was a ghost doing the rapping. In fact, he suspects it might have been the ghost of his dead loved one Lenore who was trying to gain admittance but gave up because he spent so much time in thought before responding. He calls the name "Lenore" into the darkness, but there is no response except an echo of his own spoken word "Lenore." He turns back into his chamber with "all my soul within me burning." He is frightened by the supernatural aspect of the event and also intrigued by the possibility that he might be able to become reunited with his deceased love. He is willing to be reunited with her even if she is a ghost, or even if he has to die in order to be with her once more.
Then he hears the tapping again. This time he realizes it is coming from his window. Once again he takes the more rational assumption that it is a human visitor who is tapping on the window for some reason rather than at the door. Perhaps the visitor got no response at the door so he or she went around to the window. The speaker flings the shutter open and sees that it is a raven that has been pecking there. The raven struts right inside and makes itself at home. This amuses the speaker, who tries to talk to it and who speculates about where it came from on such a stormy night. The only response he ever gets is the single word "Nevermore." No matter what he asks the bird, or what he entreats, or threatens, he continues to get the same response. "Nevermore" may be the bird's entire vocabulary, but to the narrator it comes to mean that there is no hope of ever being rejoined with Lenore in life or death. There is no balm in Gilead, no afterlife, no heaven, no resurrection. In the end the speaker is totally heartbroken and depressed.
The Raven is Poe's masterpiece. It had a profound influence on modern poetry by way of the French, especially Charles Baudelaire, who idolized Edgar Allan Poe and translated many of his works.