Final answer:
The raven saying 'Nevermore' confirms the speaker will never see Lenore again, pushing him closer to insanity.
Step-by-step explanation:
The raven saying 'Nevermore' in this excerpt propels the narrative action of the story by confirming that the speaker will never see Lenore again, pushing him closer to insanity. The repetition of 'Nevermore' further emphasizes the speaker's despair and hopelessness. This creates a sense of tension and suspense in the story, as the speaker becomes increasingly obsessed with the raven's answer.