Well first of all, the main character is grieving over the loss of Lenore at the beginning of the poem. It's a night-time during a time in history that didn't have electricity, so in my mind I see a barely lit chamber by few candles. He's in a very loney and depressed place physically, emotionally and mentally; this is only aggitated by the entrance and annoying presence of the Raven. The speaker asks the Raven where he came from, not expecting an answer, and is shocked when the bird answers. This helps to flip him out and he compensates by going off onto this tirade of speech with the bird. It takes him hearing the word "Nevermore" five times before he reaches for an alcoholic drink to help ease the madness in his head ("Quaff, oh quaff this kind nepenthe" Line 45). So the speaker goes from a sad and depressed state of mourning and ends up in a crazed, drunken state of hallucination (it would seem to me) because then he "sees" the Raven's shadow and his soul "floating on the floor" (Line 69).
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In the poem, the speaker moves from melancholy to outright despair. His initial sorrow looks to have been caused by Lenore's death; however, by the end of the poem, his unhappiness is caused by the realization that his grief is eternal.
In the poem, the Raven's words "Nevermore" is significant. Poe uses this repeated word to stress the irrevocable power of death and its ability to overwhelm one's existence. Interestingly, Poe believed that enduring melancholy was the highest form of human adulation and that sorrow for the death of a beautiful woman was closely tied to beauty of expression.
In the early stanzas, the speaker is dejected and weary. When he hears knocking, he tells himself not to hope that it's anything more than a stranger seeking entrance to his chamber. The phrases "nothing more" and "nevermore" stress the permanent nature of the speaker's sorrow: his Lenore will never grace his presence again, and thus, his soul will never be lifted from the depths of melancholy.
He prays desperately that nepenthe (a powerful ancient anti-depressant) will help him forget Lenore, but the raven ominously pronounces that forgetfulness will elude him: he will "nevermore" forget Lenore. He then pleads for "balm in Gilead," but the unrepentant raven assures him that he will never know relief from his melancholy. The speaker then tries a different tactic; he questions whether he will ever hold the "sainted" Lenore in the presence of the angels. The raven pronounces that he will "nevermore" know that joy. The despondent tone casts a mood of dark resignation over the entire poem.
So, in the beginning of the poem, the speaker is depressed. However, he still entertains a shred of hope in the deepest recesses of his psyche. He imagines that there might be a hereafter, where he may be reunited with his love. He even entertains the idea that God will relieve him of his unending, torturous grief. By the end of the poem, however, the speaker becomes resigned to his inescapable fate. He realizes with a pang that he will never be free from melancholy and that he is doomed to eternal sorrow.