What is the author's purpose in Chapter 23?

The trial of Muff Potter finally stirs up the small town of St. Petersburg and is an important turning point in the novel. One theme that is exemplified by the trial scene is the theme of "justice." Twain uses the idea of "justice" throughout the novel: Injun Joe's revenge on Dr. Robinson, Tom's thoughts of revenge, Aunt Polly's need to punish Tom. The idea that "every action has a reaction" is embodied in the legal trial. And of course, in order for justice to happen, Tom must make the decision to come forward with his eyewitness account of the murder.