In The Kite Runner, what were Amir's sin and his redemption?
I would like to know how to explain the author's attempt to show the readers how he portrays sin/redemption with his characters (Amir Khan).
You have placed your finger on the key theme of the novel. It is of course Amir's failure to protect his friend, Hassan (who also turns out to be his half-brother) from being raped that is the driving conflict of the story. Following this incident Amir feels so ashamed about what he didn't do that he "organises" for Hassan and his father to leave his household by planting stolen goods on Hassan. This is Amir's "sin", if you want to call it that. However, it is later on in his life, once he has left Afghanistan and married in the United States, establishing himself as a writer, that he is contacted by an old family friend, and feels he needs to try to redeem himself by helping Hassan. He finds out about Hassan's death for his continued loyalty to Amir's family, and also discovers the truth of Hassan's parentage. Then in his attempt to rescue Hassan's son from the same man that raped Hassan, he is very badly beaten up, but manages to leave to the United States where he and his wife adopt Hassan's son. This is how Amir finds his repentance, but you would do well to think about how this theme is much wider than just Amir.