Interaction between Montresor and Fortunato is the only thing that is advancing the plot because there is not much happening besides their dialogue. In their dialogue, we can see the hint that is showing us that the letter would be ruined and demised.
Montresor is wanting the revenge and he is trying to set a diabolical scheme because of it which is showing us contradictory in him because he is saying something that doesn't approve his acts. Since the story is told from his perspective, we are more likely on his side and we are empathizing with him.
