What are some quotes in To Kill a Mockingbird that show indirect characterization of Jem?

In chapter 16, Scout and Jem are just beginning to realize the racial stratification of their town, and as the older sibling, Jem has a better grasp of Maycomb's unwritten rules of race than does Scout:

"Well how do you know we ain't Negroes?"
"Uncle Jack Finch says we really don't know. He says as far as he can trace back the Finches we ain't, but for all he knows we mighta come straight out of Ethiopia durin' the Old Testament."
"Well if we came out durin' the Old Testament it's too long ago to matter."
"That's what I thought," said Jem, "but around here once you have a drop of Negro blood, that makes you all black."

This quote shows Jem's growing maturity and understanding of the injustices of racism. After all, Jem understands that it is impossible for any person to know the totality of his DNA heritage, and that anyone could have an ancestor of color. However, in Maycomb, if a person has a known lineage of African ancestry, that makes him black—period. Jem understands the futility of this way of thinking, but the adults around him seemingly do not.
In chapter 14, Jem makes a difficult decision when Dill runs away and hides at their house:

Jem was standing in a corner of the room, looking like the traitor he was. "Dill, I had to tell him," he said. "You can't run three hundred miles off without your mother knowin'."

In this quote, Jem has chosen to betray the confidence of his friend because he understands the inherent worry that Dill's decision will generate. He also understands that he and Scout cannot possibly hide Dill and lie to Atticus forever, so he is developing the forethought to see the long-term implications of his own decisions. Letting Atticus know what is going on now is much preferable to Atticus discovering their lies days or weeks later. Jem is maturing in thought, as evidenced in this quote.
In chapter 25, Jem shocks Scout when he refuses to kill a bug:

[Jem] was certainly never cruel to animals, but I had never known his charity to embrace the insect world.
"Why couldn't I mash him?" I asked.
"Because they don't bother you," Jem answered in the darkness.

Jem has become sensitive to noticing those creatures who are defenseless, completely vulnerable to the whims of mankind. This, of course, was brought to the forefront of his thought through Tom Robinson, but he is now extending that new understanding to other creatures as well. Jem is a compassionate and empathetic guy, learning from the world around him and seeking to make changes where and when he is able.