In Stienbeck's novel The Grapes of Wrath, most of the characters went through some type of change. Tom Joad affected many different people throughout the whole trip to California. Not only did he change as a result of the long trip, but also he had a major impact on Jim Casy and on the whole Joad family in general. The significance of these changes helped to determine the whole plot of the unfolding story. Tom's influences changed the way the characters felt and acted.
In the beginning of the novel, Tom Joad has just been released from prison for having killed a man. (Here we find him in a proud, non-regretting state of mind.) As he catches up with his family and travels many miles, his attitude changes drastically. Tom realizes the great value of a close family, so he tries to help his family to stay strong and work together to benefit each other. ?You got to think about that day, an' then the nex' day, about the ball game Sat'dy.? This quote is taken from a point in the story where Ma is unsure of what will become of their future in California. Tom reminds her that she must take things one day at a time. Their future is indefinite and unclear, but with Tom's positive attitude, the emotional stress is somewhat alleviated from everyone.
When Jim Casy first meets Tom Joad, Tom had just been released from prison. Casy used to be the preacher in the town; therefore he is a longtime friend of the Joad family. Casy has been living his life wondering around aimlessly, obtaining food by killing small animals, and living off the land. Tom asks Casy to join him in looking for his family, and on their search they come to be companions. The two find the Joad family, as they are about to depart, and Casy is invited to join the family on their excursion. At various times in the novel, Casy is asked to say a prayer to which his usual response is, ?I'm no longer a preacher.? Which in itself signifies a change in Casy. As the family is packing up to leave, Grampa decides that he is not leaving, he wants to stay on his land and live like Muley Graves does. Grampa says, ?I'll just stay right where I b'long?. Tom then takes it upon himself to think of a way to get Grampa to go. To prevent the family from being torn apart, Tom mixes medicine in with Grampa's coffee to make him sleepy, so that they can put him on the truck and be gone by the time he wakes up. After Casy sacrificed his life for Tom, Tom feels as if he is obligated to try and finish organizing the people together just as Casy had, to rebel against the government.
At times during their trek across the western states, certain members of the family would get the feeling as if they didn't know whether or not the long trip was worth the hardships and struggle. For example, when the Joads discovered a relaxing river, Noah decided that he wanted to stay there and make a life out of catching fish. Tom tried to explain that the family needed him, but it was too late, Noah had already made up his mind.
Tom Joad's experiences in jail, his trip across the country and staying in such close quarters with many different people have changed his way of thinking, and himself as a person. Essentially, Tom is a rather steady person who does not like to be pushed around. He values his individuality and his independence. So, when the cops began to push him around, he had to find something like the government camp to regain his strength. He had assured Ma Joad that he was not ?mean mad? like Purty Boy Floyd, but the more the cops pushed him around, the more Tom turns towards violence.