Forgiveness and redemption are major themes that are explored in The Kite Runner. Amir and Hassan maintain a close friendship throughout their younger years; however, Amir never loses the notion that he is more priviledged and therefore "better" than Hassan. Amir continually tries to live up to his Baba's high expectations, and as a result, his self-esteem is low. When Hassan needs Amir's help in the alley, Amir turns his back on him. Amir soon realizes that he has made the wrong decision, and he is overwhelmed by the guilt caused by betraying Hassan. Thus, Amir embarks on a journey to seek forgiveness from others and himself for being a coward. He makes decisions to help find redemption in his life--this guides his decision to raise Sohrab as his own son.
I've included a link below for several other observations concerning this question, which has previously been asked and answered.
Amir meets a girl named Soraya. She is ashamed about her experiences in the past. Soraya is ashamed that she had ran away with an Afghani man when she was eighteen, lost her virginity to him and was also on drugs. She lived with that Afghani man for a month before her father made her return home. All these experiences make her fearful that Amir would not marry her.
Baba does not tell Amir that he’s half-brothers with Hassan when he is younger. Baba feels guilty and says “forgive me if you with but most importantly, forgive yourself” (Husseini,). Baba is apologizing to Amir for not telling before, because if Baba has told him before, things could have been better between. Amir accepts his apologize.
And also at the end of the novel Amir tries to go and look for Hassan to fix everything but he finds out that he's dead so he decided to go to Pakistan and saves his sun Sohrab from Assef. He saves and takes him back with him to America