1 well developed paragraph that explains the significance of chapter 21 and its influence/contribution to the plot

By Chapter 21, Jem was sure that the trial would go in Tom's favor after all the evidence was revealed. Therefore, the pronouncement of guilt comes as a complete surprise to his naive mind, and he feels physical pain upon hearing each jury-member's "guilty". Jem is psychologically wounded by the results of the trial, feeling that his previously good opinion of the people of Maycomb (and people in general) has been seriously marred. Jem's trust in the rationality of the people has been beset by the knowledge that people can act in irrationally evil ways. He finds himself struggling to conceive of how otherwise good people can behave terribly throughout the remainder of the book.

Despite the unfavorable verdict, the black community pays tribute to Atticus for the respect he has shown their community and the human race. Atticus dedicated himself to the trial, which everyone knew was a lost cause. He tried as best he could to allow Tom to go free, and worked to teach the townspeople a lesson by exposing the unfairness of their collective opinions. Just as he fathers Jem and Scout in good moral virtues, he tries to teach the town a lesson and infuse them with more virtuous ideas.