What motifs are used and for what purpose?
There are many, as with most novels, and I will address one for you. This story is recognized not only for its literary merit, but for being the first novel written in English by an Afgan author. Thus, a strong motif centers around culture.
However, I'd like to focus on a mroe universal motif. Culture aside, this story is a coming of age story at its heart, much like To Kill a Mockingbird or Catcher in the Rye. The motif is personal identity. The protagonist, as a result of personal and social conflicts, comes to identify his own personality and beliefs about the world and how he will live in it.
Amir's conflict revolves around his betrayal of Hassan and his father's betrayal of his family. Through these two things, Amir learns how important honesty and forthrightness are to him, and he becomes determined to make things right as an adult.
It seems that people are thinking and offcourse there was something fishy which led you write this question otherwise there is no need for it.
This book was basically written and then promoted for pure political purposes and for cultural promotion purposes. Afghanistan has its own identity, history, culture, language and pure people.
The western media by all means promoted this novel to justify the US going to Afghanistan.
Secondly, this book promoted all the Iranian culture, lanugage and traditions and even their poets and stories. There was nothing from Afghanistan that any Afghan could proudly say that this novel benefitted us culturally even a bit. This book was banned in Afghanistan because it was so violently written against one major group of people of Afghanistan "the Pashtuns". Husaini has tried to prove Pashtuns as Taliban but people are not blind and crazy to trust any fiction of someone's personal frustrations.
He never lived in Afghanistan after the war started therefore, this book was the repetition of the same old tune of the news that we read and see. The book was written in a way that one felt many times as if we had already seen this seen in a movie or we could predict what would happen next.
Finally this man is a lucky one who wrote down his personal furstration in such a time where forces in Afghanistan needed to make every common person understand about why they went to Afghanistan, indirectly. And they did through Kite Runner.