By repeating certain adverbs and adding other adjectives adds to the drama and makes it more intense and suspenseful, his paranoia adds to the stress and anxiety that the narrator is feeling; for example poe could've easily written “Very cautiously” instead of “cautiously-oh, so cautiously —cautiously” to get his point across, But by repeating certain words over and over again the author creates a situation that is much more stressful, horrid and cruel.
These repetitions bring the reader and the narrator much closer together because the reader intensely feels what the narrator is going through and how he is trying to justify his actions by repeating adjectives such as “wide” in “It was open --wide, wide open.” if it wasn't for this, the reader wouldn't be convinced of what the narrator is trying to justify and make sense of. Moreover, by repeating certain words the reader can’t help but to sympathize with the killer and question his (in)sanity. it creates an anxiety and paranoia which requires a hasty action and Poe took this concept and implement it very well in the story to a point it becomes the primary force at engaging the reader with how the narrator is feeling during the course of the