In "The Raven," what does the narrator expect when he opens the door to his chamber?

The speaker expects to find a visitor there. He had been reading to take his mind off his sorrow at losing his love Lenore, and had fallen asleep. Initially, when he hears the noise, "as of someone gently rapping, rapping at my chamber door" (Stanza 1), he is startled, but he calms himself by repeating the most logical explanation for the noise to himself. Surely, "'tis some visitor entreating entrance at my chamber door (Stanza 3).