It would seem that Montresor is mainly interested in getting rid of his bad feelings about Fortunato, as opposed to getting rid of Fortunato himself. If Montresor were to murder Fortunato and then get caught and sent to prison, he would not be rid of his bad feelings. There must be many men who are suffering through long years of imprisonment after having committed a murder motivated by hatred, jealousy or revenge. Most have probably not cleansed themselves of the painful emotions that caused them to commit their crimes in the first place. Montresor is simply saying that he wants to commit the perfect crime, and the perfect crime, by definition, cannot be perfect unless the perpetrator gets away with it. Montresor is so successful in committing his murder of Fortunato that he is cleansed of his hatred.
The narrator, Montresor, is saying here that he doesn't just want to punish Fortunato, that would not be enough. He must do it in a way that will make the notion of revenge perfect and complete. This means he wants to avoid being caught for killing Fortunato, because that will undermine the very idea of revenge. In his view, revenge is simply the righting, or 'redressing' of a wrong, so that the revenger must not be punished. He further goes on to remark that there is no point in revenge unless the victim understands just why doom has come upon him, and for this the avenger has to make his identity and motive quite clear to his victim.
In holding these views on the necessity and the nature of revenge, Montresor is following his family motto to the letter: 'Nemo me inpune lacessit', which means, 'No-one injures me and gets away with it.' However, we are not told just what Fortunato did to him; it may be that he is reacting out of all proportion to the event.
In Edgar Allen Poe's "The Cask of Amontillado," Montresor forwards an interesting philosophy in regards to revenge. He states:
"I must not only punish but punish with impunity. 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.
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 in to smile in his face, and he did not perceive that my to smile now was at the thought of his immolation."
In the first paragraph Montresor states that revenge is something he "must" unquestionably do. However, he must execute his punishment while remaining free from the negative consequences of murdering a man. He then asserts that a wrong is never set right when revenge is the main aim of the individual whose goal it is to rectify that wrong. Thus revenge can never bring about justice. The term "as such" in this portion remains ambiguous. This phrase can be interpreted to refer back to the avenger, and that if the victim does not comprehend that the act of revenge is an act of revenge that wrong is not addressed in any form. These are two rules/ principles that Montresor adheres to, but they are also filled with major contradictions. Philosophically, revenge cannot make a wrong right, which is one possible definition of justice. However, Montresor executes his own kind of justice by carrying out his revenge. Futhermore, a wrong is not rectified when the victim is unaware of the act of revenge, necessitating a kind of truth, but that revenge can only be executed through deceit.
This deceit continues in the second paragraph where Montresor's behavior is a mirroring of Fortunato's, a display of excessive warmth and friendliness. Montresor matches deceit for deceit. The play on words at the end of the story, where Fortunado mentions Montresor's lack of a masonry status, and Montresor reveals that he is indeed a different kind of mason which allows him to murder Fortunado. Montresor continues this "eye for an eye" rule by matching Fortunado's offenses.