I agree completely with posts 2 and 3. I think that not only does this open Jonas' eyes to the truth of what is happening in the community and the lies that it is built upon, but I think this really shatters illusions he had about everyone in the community and their understanding of the world. He realizes that his father, who is a nurturer, who loves children, is gentle and caring, does this terrible thing, and doesn't even bat an eye. His father is so indoctrinated with the community's rules and institutions that the father doesn't even realize this is murder. To the father, and most people in the community, it is not seen as murder, but just something that must be done. I think this inhumanity was what Jonas saw and realized that he could no longer live in the community.