How does Edgar Allen Poe develop the theme in "The Raven?"

The theme of Edgar Allen Poe's "The Raven" is the slow decline of the speaker into madness. This is developed in several ways.

First, situationally. The protagonist hears a mysterious knocking noise, and when he goes to check the door, no one is there. He begins to fear, perhaps for his safety, perhaps for his sanity, as he must be making up noises in his head. 

Second, the interaction in the poem occurs inside the speaker's head and in his outward conversation with a bird. He is contemplating the purpose of the bird and its message, but does not consider as much as one might expect the implications of the fact that he is talking to an animal.

Third, the author uses repetition. In other Poe works, such as "The Tell-Tale Heart," repetition is used to imply that a character is losing his mind, as the invented heartbeat showed in that story. In "The Raven," the repetition occurs with the knocking sound, and then with the Raven continuing to say only "nevermore." The protagonist is first intruiged by, and then obsessed with WHY the Raven keeps speaking only that word. What does it mean? Why is this happening to me?

These are three ways Poe develops the theme of descent into madness in this work.