Over the course of the novel, one of the main storylines is the way that Jonas changes. He goes from being someone who completely accepts the way his society is to someone who is totally willing to (essentially) destroy it.
At the beginning of the book, Jonas has no problems with his society. He has no problems obeying the rules. His only worry is whether he will be assigned a good job.
By the end of the novel, he is thinking for himself. He has decided that the Sameness he grew up with is completely unacceptable. He is willing to go Elsewhere and release all his "memories" back into the community even though this will surely destroy it.
In the beginning of the book Jonas is a young boy who views his world the same way as everyone else in his society. There are some differences in Jonas though. He has eyes which are lighter than the others. The second difference is that when it comes time for him to be given an assignment at 12 years old, he is chosen to be a receiver. It appears that Jonas did not even know that there was such a position in his society.
Jonas begins to change from the first experience he has through the transference of the memories. The more memories Jonas receives, the more alienated from his society he becomes and the less tolerable he is of their way of life. The situation becomes so intolerable for Jonas that he decides to leave the community.
Jonas who generally obeyed the laws of the community, now makes a conscious effort to deny the laws and leave the community. He risks his life to leave the community and he takes the infant Gabriel along with him.