Why use part one and part two?

Albert Camus separates the book into two parts to show how Meursault changes throughout the book. in part one he seems to be just an insignificant human who goes through the motions and just takes what life thrown at him. he doesn't care about anything or anyone and shows hardly emotion. In part two, he is thrown in jail for killing that Arab guy on the beach so all of his freedoms are taken away. at first he says that it was hard for him because his thought were that of a free person's but he eventually got used to it. throughout part two he shows a lot more emotion and he actually seems to be alive. he reflects on his life up to this point and just changes overall. Camus just uses the two parts to emphasize that change.