Amir's return to Afghanistan comes from his realization that Hassan was more than a childhood friend he betrayed, but his half-brother. At the behest of a family friend, he resolves to find and save Hassan's own son, who is stuck in an orphanage. By helping Hassan's son, Amir hopes to remove some of his own guilt at first not helping him and then framing him for theft, causing the shaming of Hassan's father and deep grief of Amir's own father.
...my entire life, long before the winter of 1975, dating back to when that singing Hazara woman was still nursing me, had been a cycle of lies, betrayals, and secrets.
There is a way to be good again, he’d said.
A way to end the cycle.
With a little boy. An orphan. Hassan’s son. Somewhere in Kabul.
(Hosseini, The Kite Runner, Google Books)
If Amir can save Hassan's son, although he can never apologize to Hassan, Hassan's father, or his own father, he can begin to do something worthwile and make up for the pain and suffering he caused. Amir sees Hassan's son as the symbol of everything he did wrong, and desires to do something right. It won't make everything better, but it will help his own shame and guilt, and it will save a young boy who may live and die in endless suffering.
As was mentioned in the previous post, Amir seeks redemption by traveling back to Afghanistan to save Sohrab from a terrible life in Kabul. After receiving a call from Rahim Khan, Amir discovers that there is a way to redeem himself from his past mistakes. Amir has lived his entire life with the guilt of not defending Hassan while he was being raped by Assef. Decades later, Rahim Khan calls Amir, who is living in California, to tell him that there is a way "to be good again." Amir plans on traveling to Kabul and removing Sohrab from a dangerous orphanage. However, when Amir travels back to Kabul, he discovers that the Taliban has control over the entire city. In addition to seeing the dangerous state of Kabul, his old nemesis Assef has also been sexually molesting Sohrab. Amir finds redemption by fighting Assef in order to save Sohrab. Fortunately, Amir is able to defeat Assef with the help of Sohrab and they escape Afghanistan. Amir finds redemption by not only standing up to his enemy but saving Hassan's son Sohrab from a terrible life in Kabul.