At the beginning of the novel, Jem's perspectives are still quite immature. He views the world through the lens of what he's told and what he hears. Later, as he becomes aware of injustices around him, as he becomes involved in his father's case, as he discovers truths for himself, he matures into a son that his father would be proud of. We can see this culmination at the end of the novel where he stands with his father against the mob of people who've come to lynch his client.
