Steinbeck uses recurring symbols, motifs, and specific narrative episodes to link each intercalary chapter with its adjacent narrative counterparts so that the intercalary chapters, far from being an intrusion, actually unify and strengthen the dominant themes of the novel. The land turtle of the brilliantly descriptive and symbolic Chapter 3 will be picked up by Tom Joad in Chapter 4, and the dramatic monologue of a used car salesman figures immediately before the Joads' purchase of a truck for their journey west. Likewise, the Joads' search for work in California is preceded by a history of migrant labor in that state.
Steinbeck knew the importance of his readers grasping the greater social message presented in The Grapes of Wrath. The suffering of the wandering families and their oppression by larger, more powerful forces was a social crisis of widespread magnitude. He was concerned that readers would not comprehend this urgent, yet impersonal problem unless they could focus their sympathy on the ordeals of a specific family. At the same time, however, he did not want the struggles of the Joads to be considered isolated events, specific only to a particular family. The use of intercalary chapters provides a balance, allowing Steinbeck to realize the ultimate artistic goal: To weave together specific social facts and lyrical elements to create a personal story that expresses universal truths about the human condition.
