On the fast track to madness due to the loss of his lover Lenore, the speaker in Edgar Allan Poe's poem "The Raven" would like nothing more than for the raven to give him good news about her return. When he asks the bird if he and Lenore will be reunited in Heaven, it accordingly responds "Nevermore!" Unhappy at the response, the reader demands that the raven leave him alone and get back to the "Plutonian shore" (return to the Devil). However, the bird refuses to leave, again remarking "Nevermore!" and continues "still sitting" on its perch on the bust of Pallas above the chamber door.
The speaker begins to ask the raven questions about Lenore. He wanted to know whether they'll be reunited. He also asks where it came from (specifically if he was with the devil). All the raven does is reply with "Nevermore!"
The poem seems to me metaphoric. The narrator is having a hallucination. After he has spent most of the evening in sadness; to try to lift his spirit, he takes the drug nepenthe and ends up on a "trip." On this "trip," the raven flies into his "window" -- his soul. The raven is black -- like his mood and his very soul because of losing Lenore. The "door" is his heart -- the tapping his heart beat. The "raven" or sadness/blackness is as lasting and enduring as the cold and stony bust of Pallas -- which means he will never be free of the memory of Lenore.