Why is it surprising to Farid that Amir would search for Sohrab? What do you think this reaveals about Farid?

Initially there was a division between Farid and Amir. When the journey to rescue Hassan's son began they did not talk. Farid had resentment against Amir until he learned that Amir was not in Afghanistan to just sell his father's property and return to America. He learned that he was there to rescue his illegitimate half brother’s son, a Hazara, and this surprised him. The most important thing we learn about Farid is how selfless he is in helping others and doing what he believes to be the right thing. But he won't do this for everyone, only those he feels a bond of loyalty to.