What is the importance of the lengthy description of changes that Amir finds on his way to Kabul and in the city itself?

The importance would lie in Amir's complete comprehension of the changes in his homeland. It is one thing to escape, and another to hear about the atrocities while you live far away from them.... it's a whole other story to see the reality first hand. At that moment, Kabul stopped being a memory from childhood...... it became a true and real tragedy.