What is the theme of Edgar Allan Poe's story "The Cask of Amontillado," and how does the story relate to the theme?
Though I am sure there are more deeply rooted themes in “The Cask of Amontillado”, the two most obvious seem to be Revenge and Atonement and Forgiveness. As to how they relate to the story, revenge is quite obvious as Montressor commits the ghastly and extremely well planned out murder of Fotunato in his drive for revenge against injuries he believes Fortunato has caused him. The notion of seeking revenge is mentioned several times throughout the story. The second theme, that of atonement and forgiveness falls entirely upon Montressor. Although he felt vindicated in what he had done to Fortunato, he could only atone for his sins and be forgiven by God himself, and that idea is left in limbo by Poe.
The theme of Poe's wonderful story is revenge, though I'd probably narrow that a bit: the overwhelming intensity of revenge and how it can distort and destroy lives. The story relates to this theme on both the literal and the psychological level. Literally, Montressor bricks Fortunato into the walls of the catacomb and kills him. On the psychological level, the mysterious "thousand injuries" that Fortunato has done to Montressor have unbalanced him, turning him from a harmless wine snob to a killer.
In the story, it isn't enough for Montresor to simply exact revenge on and kill Fortunato. He has a very specific idea of what this revenge must entail. He says, "A wrong is unredressed when retribution overtakes its redresser. It is equally unredressed when the avenger fails to make himself felt as such to him who has done the wrong." Thus, Montresor cannot incur any punishment as a result of his revenge, and he must make it known to Fortunato that it is he, Montresor, who is responsible for Fortunato's fate. If he is punished somehow or fails to make his responsibility known to his victim, then he will consider the revenge null. This, for Montresor, his revenge is a point of pride. It is his pride, personal and even familial, that has been wounded, and so he feels that he must avenge those wounds in order to maintain his honor. Only pride would require him to make his role in Fortunato's fate known to the man before his death. Therefore, pride is a major theme in this story as well.
In addition to pride, this story explores the nature of guilt. Montresor tells his tale to someone who "know[s] the nature of [his] soul" some "half of a century" after the events occurred. Thus, it stands to reason that he is now an old man confessing his sins to a priest (someone who would know his soul). If the sin has burdened him for so long, then did he really exact his revenge without punishment? Some would argue that he has not. Is guilt punishment enough to negate his completion of his revenge? The story thus takes guilt as another of its themes.