One of the themes in Poe's "The Raven" is alienation and loneliness. This is a result of the speaker's loss of Lenore.
The literary device that most conveys this theme is repetition.
The name "Lenore" is used over and over again. So the reader is acutely aware of the speaker's sense of love. "Nothing more" is also repeated at the end of six stanzas. It seems to refer to the lack of some thing. For instance:
‘Tis the wind and nothing more!
There is nothing outside to create the tapping at the window: only the wind. At the end of another stanza, there is only an echo of the speaker's words:
This I whispered, and an echo murmured back the
Merely this and nothing more.
The idea of nothing more can also infer that with Lenore gone, there is nothing else..."nothing more." Soon this phrase is replaced with the repetition of "Nevermore." This also alludes to the loss of Lenore, but here we can sense an even deeper sense of loss that will last for the rest of the speaker's life. He will never see her or hold her again.
The sense of isolation is also found in other repetitions of similar sounds. One device that reflects this is onomatopoeia, which is the use of a word that represents a sound. In this case, we hear "rapping" and "tapping." The words stand out because there is no other sound. The house is empty except for the speaker. There is no family about, no bustle of servants, no barking of dogs. The silence is overwhelming, so the noise at the window or door likely rings through the empty house. Even the manner in which the speaker talks is described using onomatopoeia—and again reflects the absence of caring enough to rouse himself when he "muttered." These kinds of words convey emptiness and loneliness.
There are more literary devices that depend on sound: one in particular is alliteration. This is the repetition of a sound at the beginning of words clustered together. One instance occurs at the beginning of the poem:
...weak and weary...
Here the "w" sound is repeated. It is not just that the letters are the same—the sound is the same, and this is crucial!! The sound of the "w's" used supports the sense of the reader's lack of energy, perhaps even interest. It makes one feel the author's despondency and aloneness.
Alliteration is found again in the following phrase, and this example also gives the sense of despondency—note the repetition of the "n" sound:
...nodded, nearly napping
The final eleven stanzas leave the reader (using repetition) with the sense of abject misery and loneliness with the use of the word "Nevermore." However, as the poem has continued, the reader understands that while the speaker is devastated by the loss of Lenore, he has come to feel comfortable in that aloneness. He would rather be alienated from the world and live alone to contemplate life's emptiness than to live out in society to be forever reminded of the absence of his love in his daily routine. He lives secluded and alone, with only sounds echoing through his house—and his heart, to remind him that Lenore is lost to him forever.