In the story of Cain and his brother Abel, found in the fourth chapter of Genesis, Cain, an imperfect human and son of Adam and Eve, slew his brother out of jealousy. When God asked Cain where his brother was, Cain replied, "Am I my brother's keeper?" God knew Cain murdered his brother and sentenced Cain to walk the earth as a wanderer. When the loneliness was too much for Cain to bear, he begged God to kill him and put an end to it, but God forbade anyone to kill Cain because he must be punished for breaking God's law.
This story has many parallels in Of Mice and Men. The first parallel is the question of Cain, "Am I my brother's keeper?" Steinbeck essentially asks this same question in his other works such as The Grapes of Wrath or East of Eden when he wonders if mankind should go alone in the world or be responsible and helpful to others who are less fortunate. In the character of George, the answer seems to be the latter. George takes responsibility for Lennie, and Lennie depends on him. Furthermore, the noble characters — such as Slim — are those that recognize and honor this responsibility.
When George kills Lennie, he is sentenced to be like the other migrant hands, no longer traveling with someone he loves and no longer with goals or a dream of a different future. George is sentenced to the scenario described by Crooks when he told the others that no one ever gets their dreams. George will now wander from ranch to ranch, alone like the other migrant workers, and he will live the nightmare he described when he talked about his life without Lennie: no companion, no roots, no future.
