The trial of Tom Robinson is the most enlightening event that has occurred during Jem's and Scout's lifetimes. Before the trial begins, the children come to understand its importance by picking up bits and pieces of information from the townspeople. Scout is forced to defend her father from the taunts of her classmates before finally asking Atticus the definition of "nigger-lover;" Jem hears the same words from Mrs. Dubose. Scout has heard another word which she does not understand, and she also questions her father about "rape." Much of the events leading up to the trial are beyond young Scout's scope of understanding, including the night at the jail when she unknowingly helps to save Atticus from the lynch mob.
During the trial, however, both Jem and Scout are able to follow their father's path of questioning. They understand that only a left-handed man could have inflicted the injuries upon Mayella; that father Bob is left-handed; and that Tom's left arm is crippled. Tom seems humble and honest, and the Ewells reveal themselves as Atticus had earlier described: "the disgrace of Maycomb for three generations." But the jury doesn't see things as clearly or in the color-blind manner of the children.
... in the secret courts of men's hearts Atticus had no case. Tom was a dead man the minute Mayella Ewell opened her mouth and screamed.
The guilty verdict bothers Jem most, and he loses faith in the jury system and in the people of Maycomb. Both of the children worry about the threats made by Bob Ewell and worry for their father's safety--not realizing that they, too, are in jeopardy.