Differentiate the definition of justice between Sarty and Abner, and explain the motives of each character.
Basically, Abner lives by his own rules, and Sarty by societal rules. Abner is filled with hatred and a sense that he has been short-changed in life. One might say he has a chip on his shoulder, but Abner's is more like a giant oak. When he is brought before the court, we immediately see that Abner is the judge, jury, and executioner when he feels he has been wronged in any way.
Consider these lines in which the judge finds there is not enough evidence to convict Abner: "This case is closed. I can't find against you, Snopes, but I can give you advice. Leave this country and don't come back to it."
His father spoke for the first time, his voice cold and harsh, level, without emphasis: "I aim to. I don't figure to stay in a country among people who..." he said something unprintable and vile, addressed to no one."
Sarty, on the other hand, who does not believe in his father's sense of violent retribution and justice under his own law. When Sarty wants to stop him from the burning, and his mother obey's by holding him back, he breaks free. Desperately Sarty tries to save the barn he knows his father is about to torch. Running as fast as he can, he finds De Spains servant and pleads for help: "De Spain!" he painted, "Where's...." then he saw the white man too emerging from a white door down the hall. "Barn!" he cried. "Barn!"