The extent to which Jonas resists his society in The Giver accelerates over the course of the story. It starts slowly and then builds gradually, until the end, at which point his resistance is complete.
As the story opens, Jonas is a fairly compliant child who does not question the rules, but even in the first chapter, we see a little reluctance on his part when he does not want to share his feeling with his family at the sharing ritual. We are told that "he almost would have preferred to keep his feelings hidden" (9), but then he does share his feelings of apprehension, because "of course, it was against the rules" (9) to not do so. We also see in Chapter 3 that at some point previously, Jonas has "stolen" an apple and taken it home, which was against the rules as well. Jonas is completely perplexed about why he even broke the rule, something that does get explained later on in the story.
However, by the end of Chapter 4, Jonas is questioning the community's rules, at least a little. He begins to wonder what exactly happens when a person is released, and this shows us that he is no longer taking the community's rules and processes for granted. In Chapter 5, after he experiences his first stirrings, he is given the pill that makes them disappear, and he wants them back, these feelings of pleasure that are a normal stage of development the rules deprive him of.
When Jonas is appointed the Receiver, he is actually given dispensation from some rules. For instance, he may be rude and he may lie. He finds lying to be a terrifying idea, but this is the beginning of the acceleration of his disobedience and fight against the community. And the more memories he gets from the Giver, the more it causes him to question and resist. This is because he is gaining knowledge that was forbidden to him, allowing him to see there are choices beyond the very limited choices he had been permitted to make before. When the Giver shares the memory of color with Jonas, for example, and explains why color has been taken away from the community, Jonas' response is "We shouldn't have!" (p. 95). The more Jonas learns from the Giver, the more unhappy he is with what the community has done to people. He comes to understand there are no choices for the people, and he resists that idea fiercely, now that he sees there are choices. He begins to feel angry and asks the Giver why they cannot seek changes in the rules.
I think that Jonas' resistance starts to become really strong when the Giver shares with him the feeling of love. He finds it indefensible that people should be deprived of such a feeling, and he begins to share his feelings with the baby Gabriel, saying that "there must be a way for things to be different" (128). When the Giver shows Jonas Jonas' father releasing an infant, the horror of this triggers Jonas' complete rebellion. He refuses to go home at all, and it is at that point that he and the Giver begin to plot his escape from the community, which is, of course, the escape with which the book ends.
Jonas' opposition to the rules and his ideas about changing the community begin slowly. But the more knowledge he gains, the better his understanding of what the rules of the community cost him and all the other people in the community. When he finally understands that he has been deprived of love and that people are euthanized when no longer useful, he understands that he must act against the community.