Since I think that one of the most important themes in the novel is the idea of sacrifice and taking action, I think that the rape in Chapter 7 and the confrontation in Chapter 22 are probably two of the most important events in the novel. When Assef and his buddies sodomize Hassan with Amir watching, it forms the crux of the novel. The need to "become good again" arises from this instant of cowardice. Amir's inability to demonstrate loyalty and support of his friend in the most painful time of need is something that ends up haunting their friendship. It is the pinnacle moment that Amir goes back to time and time again. It acquires even greater significance when Amir has to fight Assef for Sohrab. The same situation is played out, only this time, Amir has the courage to set right what was wronged years ago in being able to rescue Amir's son from Assef's cruelty. It makes sense that while Amir is being brutally beaten he starts to laugh. This is the moment when Amir recognizes the opportunity to "become good again" and also embraces both the sins of his own past as well as the potential for redemption in the future.