A question you can use to develop your thesis would be, "If one believes in forgiveness, why is revenge so prevalent?
Examples of themes;
Love of one's enemies is one of the novel's religious themes and deals with forgiveness. Jeremiah responds to the superintendent who mistreats and humiliates him with grace and forgiveness. The obnoxious traveling salesman Lurvy is accepted into the household. Jeremiah even comes to terms with the family's sworn enemy Mr. Andreeson, the federal investigator who is on Davy's trail. This eventually transforms Reuben's attitude toward the investigator as well. Love and forgiveness win over revenge. Davy's continued life on the run from justice, while having a certain romantic charm to it for those intrigued with stories of western outlaws, misses out on the fullness of life that is enjoyed by the rest of the family—even in the face of tragedy. (1)