Jem stopped Scout from killing a roly-poly. Relate this to the major theme of the book.

Scout sees a roly-poly bug and goes to kill it. Jem stops her, saying the bug never did anything to harm her. Scout heeds his request and carefully takes the bug outside, noting internally that if anything, Jem is becoming more like a lady than she is. I think that Jem is becoming more sensitive to the sanctity of life. He, like his father, abhors by violence in whatever form it is.