Based on descriptions of the bird, what can the Raven symbolize?

The narrator of Edgar Allan Poe’s “The Raven” describes the bird at length in stanzas seven and eight. He describes the raven as “stately . . . with the mien of a lord and lady.” The bird exudes calm as well as power. The raven also has a “grave and stern decorum” and chooses to perch on a bust of Pallas, meaning Athena, the ancient Greek goddess of wisdom. These descriptions and references indicate that the raven is there to say something both honest and important. The raven brings knowledge, specifically a form self-knowledge for the narrator through memory.
After the raven enters the room, the narrator begins thinking about Lenore, about missing her and whether she is in a better place. The raven triggers the narrator’s memory as well as his regret. Yet the narrator later describes the bird as a “prophet” at the same time he calls it a “thing of evil.” By the end of the poem, the raven’s eyes “have all the seeming of a demon.” Think about what Poe might be suggesting about memory and self-knowledge by connecting all of these descriptions together. Does the raven make the narrator think about things that help him or hurt him in the end? Is the narrator better or worse off after exploring his memory and feelings?
Poe also includes other descriptions that may seem brief or obvious. Yet remember that Poe chose to include these terms, so it is worth thinking about them further. For example, the first time we hear about the raven it is “gently rapping, rapping” at my chamber door. Why would Poe pair a description like “gentle” with repetition of the forceful word “rapping?” Also, the raven may enter gently, but does it still have a gentle presence by the end of the poem? Poe also makes sure to describe the bird as “ebony,” meaning dark. The reader could have assumed that a raven would be dark, so why does Poe deliberately remind the reader of this fact? What does darkness symbolize, especially in the context of the narrator remembering someone he loved who has died late at night?