How does the point of view influence our understanding of the story? How does the narrator’s interpretation of events reflect his or her own interests and desires?

Montresor is so adept at hiding his feelings that, were the story narrated by Fortunato, it is unlikely that we'd know what Montresor was up to until the very end. The story, then, would really lack the tension it now possesses as a result of the dramatic irony. We know, because Montresor has said so, that he intends to exact some terrible revenge on Fortunato, and so we are waiting for it, as tension builds throughout the story, but Fortunato doesn't know. As Montresor says,

It must be understood that neither by word nor deed had I given Fortunato cause to doubt my good will. I continued, as was my wont, to smile in his face, and he did not perceive that my smile now was at the thought of his immolation.

Fortunato does not know what Montresor's intentions are—in fact, no one does—and so it would be a much less exciting tale were it narrated by another character. Further, not even Montresor's servants know what he's up to because he's cleverly manipulated them to get them out of the house. He's told them that he'll be gone all night and that they shouldn't go anywhere, knowing that these instructions were enough "to insure their immediate disappearance, one and all, as soon as [his] back was turned." Moreover, he's disguised himself with a "mask of black silk" and a long cape—it is the Carnivale season, when people wear costumes to public celebrations—so that he cannot be identified. There is, literally, no one else who can tell this story with all of the drama and tension that Montresor can because he's gone to such great lengths to conceal his intentions and plan. When he says that he's been Fortunato's victim, that he's endured some "thousand injuries" as well as terrible "insult" from Fortunato, his own desire to justify the murder he's committed is clear.

Montresor is this story's narrator, and he is quite different than most narrators that readers come into contact with. Most readers assume the narrator is going to be a "good guy" and trustworthy, but Montresor lets readers know right from the beginning that he is neither of those things. Montresor tells his readers that Fortunato has wronged him, and now Montresor needs to kill him. The second paragraph lets readers know that Montresor is a good actor and a liar:

It must be understood that neither by word nor deed had I given Fortunato cause to doubt my good will. I continued, as was my wont, to smile in his face, and he did not perceive that my smile now was at the thought of his immolation.

Montresor acts like everything is great all while planning Fortunato's future immolation (sacrifice). What this information serves to do is make Montresor untrustworthy. We know that he has evil plans, and we know that he is good at deception; therefore, how can we really trust him in the first place? All that we can really be sure of is the fact that a person should never wrong Montresor. He is the kind of guy to always act in his best interests, and his friendship with somebody is likely veiling some other hidden agenda.