In the first half of the book, what are Amir's responses to the various crises with which he is confronted? These are tests of his character, don't you think? What happens in the latter part of the book when he is confronted by crises? These are tests of his character, too. One significance of the crises in the novel lies in the response of Amir to the crises. Can you contrast his thoughts, feelings, and actions in his earlier years to his thoughts, feelings, and actions later on?
Also, you might want to think about the symmetry in some of these crises. For example, what other character is involved in two central crises, one early and one later? What is similar about the evil that Amir runs from in the early crisis and confronts in the later one? There are many such symmetries in the novel, and this is a significant one.