why must Amir go to Pakistan following his phone call?

Chapter Fourteen opens in June of 2001, when Amir received a call from Rahim Khan. He told Amir he was very sick and asked him to come visit him in Pakistan. Amir considered what Rahim Khan had said before hanging up, "Come. There is a way to be good again." Suddenly, he understood that Rahim Khan knew, and had always known, what he did to Hassan. Amir was comfortable leaving Soraya with her parents; her relationship with them had improved in the years since the wedding. The General no longer insisted that Soraya change her career path away from teaching; sometimes he sat in on the classes Soraya taught and even took notes. That night, Amir dreamt of Hassan as he had seen him right before the rape, shouting, "For you, a thousand times over!" A week later, he left for Peshawar, Pakistan.