Why is Hassan's letter so important to understanding Amirs feelings in the Kite Runner?

Hassan's letter is important because it serves as a reminder of the deep bond and loyalty Amir shared with Hassan. Reading the letter triggers Amir's guilt, stirring up complex emotions about his betrayal of Hassan and his failure to stand up for him. The letter's contents highlight Amir's internal struggle, as he comes to terms with his past actions and seeks redemption.