In a way, the final confrontation between Assef and Amir is the battle between good and evil. Interestingly enough, I find that the most significant element of this confrontation is that this dynamic of condemnation and redemption takes place within Amir. Assef is the physical manifestation of Amir's dark side, the element of his nature that caused him to be silent while watching Hassan being sodomized and for persecuting Hassan in Amir's own way. The desire to "become good again" is something that has driven Amir back to Afghanistan. It makes sense that in order to fully redeem himself, Amir has to confront Assef. One way or another, the narrative is going to find resolution. The conflict between both forces help to supply the redemption that Amir seeks. The results of the conflict feed this end in that Amir suffers a facial disfiguring like Hassan and that he is brutalized in much the same way Amir was in terms of being forlorn during his degradation without much in way of support. Sohrab's use of the slingshot to finish off Assef is Amir's sign that he has been redeemed, as Hassan's weapon is used to save him. In this confrontation, the final step of Amir's redemption is recognized, making it extremely significant to the progression of the story.