what is the real reason rahim calls for amir to come to pakistan? chapter 15

Rahim Khan told Amir that he did not have long to live. He laughed at Amir's offer to take him to America, saying he accepted his fate. Then he revealed to Amir that for all the years he lived in Baba's house after 1981, Hassan lived there with him. He told Amir that he needed a favor of him.