In John Steinbeck's The Grapes of Wrath, thousands of people have have lost their jobs, their homes and their land, and have been forced to pack up and move across the country, looking for work and a new home where they can begin again.
Ma Joad, the woman who works extremely hard to keep her family and her extended family healthy, fed and together, knows how important it is to maintain a sense of unity.
There are several reasons for this. Being united is safer: the group is less likely to be harassed/robbed if they stick together. Working together also increases the chances that the group will survive in terms of finding work and/or food. Unity is extremely important to provide a sense of belonging that fights the insidious feelings of alienation brought on by this terrible time in U.S. history.
In terms of unity, one of the major themes is man (or the individual) vs society. For instance, when the men try to get work, they are often competing with others, and "fighting" even those who are hiring, for there are many man, many hungry families and only a few jobs.
Commitment is another theme, and this is easier to apply oneself to if part of a strong collective family-like unit—and that is what the Joads are. They understand that in order to survive, they must stick together. Those who do not remain will most likely die. However, there is another side to the question of commitment: in being devoted to the family, two members of the group are considered "Christ-like" figures in that they "sacrifice" themselves for the good of others.
Greater than a commitment to survive is Jim Casy's sense of obligation to others. To live by his conviction to love everyone, he sacrifices himself to the authorities so that Tom and Floyd are not arrested. Speaking to Tom of a sense of his personal duty, Jim says:
An’ sometimes I love ’em fit to bust...
Ironically, it seems that Jim's way of looking at the world (along with his experiences on the road) change Tom. Formerly a character with no desire to connect with others, he becomes an activist to fight for the rights of the downtrodden and weak.
Tom is taking a very dangerous risk in this especially desperate and volatile segment of U.S. history. The Depression had changed people who can no longer even recognize themselves as they struggle to find a way to live—for themselves and their family members. When Ma Joad worries about Tom being killed, he recognizes the possibility, and then delivers the following famous passage:
Then I’ll be ever’where—wherever you look. Wherever there’s a fight so hungry people can eat, I’ll be there. Wherever they’s a cop beatin’ up a guy, I’ll be there. If Casy knowed, why, I’ll be in the way guys yell when they’re mad an’ I’ll be in the way kids laugh when they’re hungry an’ they know supper’s ready. An’ when our folks eat the stuff they raise an’ live in the houses they build—why I’ll be there.
There is sadness in that this shows a real possibility of what might happen to Tom as he fights for social change—for back then, it was a "war," not a discussion. However, there is also the sense of hope (another theme) that the Joad family and the entire country will survive these trials, and finally able to care for themselves and each other as they used to. Unity is what will guarantee this, whether it is that of a family or that of a group of citizens determined to change the Depression-ravaged world into a new, better place to live.