Much is revealed about Jem's character in this chapter. We, for example, learn that he has outgrown Dill and Scout, for he does not hang out in the treehouse with them anymore. This is meant not only in a physical sense, but also alludes to his intellectual growth. He has reached a point where he deems it inappropriate to be around them:
Jem had outgrown the treehouse, but helped Dill and me construct a new rope ladder for it . . .
He also, on a Sunday afternoon, did not play with them as he used to, as Scout somewhat wryly observes:
Jem in his old age had taken to his room with a stack of football magazines.
He is clearly also more stubborn than ever, for when his Aunt Alexandra asks him to turn on the lights in the living room during a visit by Heck Tate and a number of other men, he pretends not to hear her because he wants to observe events on the outside from the darkness of the room so that he is not seen.
Jem also displays an astute awareness of what is happening around him. He is able to derive information from events which he would otherwise have ignored. After Atticus' visitors have left, he asks him:
“They were after you, weren’t they?” Jem went to him. “They wanted to get you, didn’t they?” Atticus lowered the paper and gazed at Jem. “What have you been reading?” he asked. Then he said gently, “No son, those were our friends.” “It wasn’t a—a gang?” Jem was looking from the corners of his eyes.
Since his father was involved in a controversial case which had drawn much attention and more than a bit of acrimony, Jem thought that the men had come to threaten him. He believed that they were ganging up against his father. He could also read from his aunt and his father's argument, as well as from the men's arrival, that there was some danger, and he told Scout that he was scared.
This also displays a more concerned attitude from Jem, for he ventures outside to see where Atticus was heading when he takes the car. He allows Scout to accompany him and when they see Atticus at the jailhouse, Scout wants to run to him, but he stops her.
I made to run, but Jem caught me. “Don’t go to him,” he said, “he might not like it. He’s all right, let’s go home. I just wanted to see where he was.”
Later, when there is a clear threat against his father, Jem displays courage and a stubborn refusal to leave Atticus' side. Atticus asks him to leave, but he does not.
“Go home, I said.” Jem shook his head. As Atticus’s fists went to his hips, so did Jem’s, and as they faced each other I could see little resemblance between them . . .
In this scene, we are also given a physical description of Jem:
Jem’s soft brown hair and eyes, his oval face and snug-fitting ears were our mother’s, contrasting oddly with Atticus’s graying black hair and square-cut features, but they were somehow alike. Mutual defiance made them alike.
Jem obviously has inherited a trait from his father—they are both defiant in the face of danger, which speaks to an inherent courage possessed by both. Atticus expresses pride in his son after things have calmed down and the mob who had come to face him have left. Scout observes the following at the end of the chapter:
Atticus and Jem were well ahead of us, and I assumed that Atticus was giving him hell for not going home, but I was wrong. As they passed under a streetlight, Atticus reached out and massaged Jem’s hair, his one gesture of affection.