The chapters located between the Joads' story are called "intercalary" chapters, and they remind us that this is a story bigger than one family. These chapters in The Grapes of Wrath by John Steinbeck serve two major purposes.
First, they draw a picture of the world as the Joads are living in it. They explain what living in the dust bowl was like, what Route 66 was like at the time of the great migration West, and the conflicts in the relationship between landowners and workers.
In the water-cut gullies the earth dusted down in dry little streams. Gophers and ant lions started small avalanches. And as the sharp sun struck day after day, the leaves of the young corn became less stiff and erect; they bent in a curve at first, and then, as the central ribs of strength grew weak, each leaf tilted downward. Then it was June, and the sun shone more fiercely. The brown lines on the corn leaves widened and moved in on the central ribs.... The air was thin and the sky more pale; and every day the earth paled.
The descriptions in these chapters highlight and illuminate the plight of the Joads. We feel badly that the Joads lost their land, but how much worse is it to know that this is the land they were struggling to keep and work. Staying and going, then, are both awful options.
Second, these chapters remind us that what is happening to the Joads is happening to thousands of others across the country. If this novel were just about one family's plight, we would not be thinking as much about all the others who are in exactly the same situation.
Some people see the intercalary chapters as a waste of time or, even worse, as digressions. The truth is that these chapters affirm and intensify the Joad's experiences. When the man and his son go into a diner in chapter fifteen and they only have ten cents to spend, that could be the Joads--or thousands of other families. When the man refuses to take more than he can pay for, that is the spirit of the Joads and those like them. And, when the waitress, cook, and truck driver do a kindness for the man and his son, that is an experience that is also happening during this time.
The same is true in the negative, of course. When the used car salesman cheats and disrespects these poor people in chapter seven, for example, he is cheating and disrespecting all of them.
The later intercalary chapters tell us things we could not know about the farms and the landowners because the Joads never really get to see them. In chapter twenty-five, Steinbeck records the struggles the small farms are also having with the big landowner farms.
And the pears grow yellow and soft. Five dollars for forty fifty-pound boxes; trees pruned and sprayed, orchards cultivated, pick the fruit, put it in boxes, load the trucks, deliver the fruit to the cannery, forty boxes for five dollars. We can't do it. And the yellow fruit falls heavily to the ground and splashes on the ground. The yellow jackets dig into the soft meat, and there is a smell of ferment and rot.
This shows others who are also struggling against the giant farms and corporations which will soon control all of the agriculture in California. These farmers may soon be competing with the Joads and others for work, but they might also be fellow labor union members for Tom to recruit.
The intercalary chapters are a valuable tool in helping us put the Joads story into context and perspective. The edsite chart (linked below) is helpful to see this.