Here's why:
* The Raven's Appearance: The raven's black plumage and dark, ominous presence directly reflect the narrator's grief over the loss of Lenore. The raven's color is associated with death and mourning, adding to the atmosphere of despair.
* The Raven's Repetition: The raven's constant repetition of "Nevermore" serves as a relentless reminder of the narrator's loss. The word echoes the narrator's inability to move on or find solace.
* The Raven as a Messenger of Despair: The raven's presence acts as a catalyst for the narrator's descent into madness. Its ominous appearance and chilling pronouncements exacerbate the narrator's already existing grief and drive him to the brink of insanity.
* The Raven as a Symbol of Hope Denied: The narrator initially hopes that the raven might offer him some solace or answers regarding Lenore's fate. However, the bird's constant "Nevermore" shatters these hopes, leaving the narrator with a crushing sense of despair and hopelessness.
While other elements in the poem, like the "grim, ungainly, ghastly, gaunt, and ominous bird" and the narrator's inner turmoil, contribute to the overall theme of loss and sadness, the raven itself stands out as the most prominent symbol of the narrator's emotional state.