After witnessing racial injustice for the first time, Jem loses his childhood innocence. He is deeply hurt by the outcome of the Tom Robinson trial and becomes jaded with the prejudiced community of Maycomb. At the end of Chapter 23, Scout and Jem are having a discussion about the various types of "folks" in their community. Jem tells Scout that he used to think there was only one kind of folks, but cannot understand why they don't get along with one another. He goes on to say,
"I think I'm beginning to understand why Boo Radley's stayed shut up in the house all this time...it's because he wants to stay inside" (Lee 139).
One of the prominent themes throughout the novel concerns the idea of prejudice. Throughout the Tom Robinson trial, Jem witnesses the destructive nature of hate and prejudice. Following the trial, Jem sees his neighbors as prejudiced individuals. He is disgusted with their decision to wrongfully convict an innocent man and does not want anything to do with them. Jem does not blame Boo Radley for not coming out of his home because he understands the dangers of prejudice and hate that exist throughout Maycomb.
The discussion between Jem and Scout is at the end of chapter 23. The outcome of the trial has left the children reflective on the character of people. Jem has been thinking of Boo, and has figured out why he is a recluse,“I think I’m beginning to understand why Boo Radley’s stayed shut up . . . it’s because he wants to stay inside.” The harsh prejudices that the trial have brought to life have given Jem the perspective that hiding away from the ugliness is Boo's defense mechanism.
This declaration comes right at the end of chapter 23. After talking with Scout, who Aunt Alexandra spent much of the chapter trying to impress upon what it means to be a Finch, Jem comes to the conclusion that Maycomb has a caste system where people are ranked not just by money but also by familiar history, race, color, education, and so on. When Scout tries to make sense of this she declares that there is just one kind of folks, and this just plain old folks. This prompts Jem to state that he knows why Boo stays inside. We can infer that Jem means Boo stays inside to avoid all of the classification and discrimination in Maycomb. He can avoid it all by just staying shut up in his house.