Poe personifies the raven so that the bird can perform a function within the poem. In speaking to the raven, the narrator reveals himself, the innerworkings of his mind as he struggles with grief and despair. Throughout the poem, the raven does not change, but we see the narrator move through a variety of emotions, including fear, anger, and deep sadness.
Also, by personifying the raven, Poe adds an element of mystery and suspense to the poem. Where did it come from? Why is it there? What is it thinking? The power of the poem, however, is found in this idea. The personification of the raven occurs only in the narrator's mind. It is he who finds human traits in the raven. Essentially, the bird does nothing except speak one word it has learned somewhere, if it even speaks at all. For the narrator to seek conversation with the raven indicates the depth of his desperation during the lonely night.