What is the speaker's explanation of the raven's one response?

At first, the narrator accounts for the raven's one word, "'Nevermore,'" by thinking—logically—that "'what it utters is its only stock and store" (line 62); in other words, the bird speaks the only word that it knows. He assumes that the bird's owner must have endured a number of "unmerciful Disaster[s]" after which he spoke this word many times, and he believes that this must be how the bird learned the word (63).

However, the narrator begins to think that the bird's presence and speech might have some deeper meaning.  First, he wonders if God actually sent the bird to him to distract him from and help him to forget his grief over the "'lost Lenore!'" (83). Perhaps the bird is a kindness. He says to himself to enjoy this opportunity to forget his sorrow, but the raven replies, "'Nevermore,'" which enrages the speaker.

Then, he wonders if the bird is a "'devil'" sent to tempt him, perhaps, to his own death (85). Maybe the bird is a "'Prophet,'" he thinks, of death, and so he asks the bird if there's a chance that he will ever see his lost Lenore again, in the eternal life after death. The raven, of course, says, "'Nevermore,'" making the narrator very angry and desperate at the idea that he can never be reunited with his love.