I would think that a thesis statement for The Grapes of Wrath would need to include something about the need for workers to unite and work together to achieve better wages and working conditions. The book moves relentlessly in that direction, as the Joads travel to California and try to make their way in a hostile environment that is dominated by rich landowners.
You may wish to read the enotes page on themes. One of the stated themes is that of social commitment. Another theme, that of exploitation of the common people by the distant wealthy who own the millions of acres of land in California and the banks is greatly expanded with the intercalary chapters. So, perhaps you could demonstrate how these chapters further a theme.
It depends a lot on what theme you want to focus on. Let us remember that Steinbeck wrote this novel to partly comment upon the way that man exploits his fellow men in times of hardship and need. There is thus a very distinct social commentary in this excellent text that you could write about. An appropriate starter to your essay that would hook your reader in therefore might be:
Throughout history, man has displayed the sad propensity to exploit his fellow man in times of hardship.
This would allow you to go on and present this theme and write your essay. Good luck!
Given that one of the main themes of the novel is hope, you could link your thesis statement (and essay) to the journey the character/s went on in order to find the hope they needed to survive.
Therefore, a possible thesis statement would look something like this:
The journey for hope, in The Grapes of Wrath, led the character/s on a path which allowed them to look for a new way of living life.
Here's a topic that I think is relatively unexplored: the humor encountered and experienced during the journey. Many people think of the journey as grim, solemn, and depressing, but in fact there are a number of very funny episodes and characters in this book. Taking a close look at how they contribute to the complexity and success of the book might be a good approach. Good luck!
In order to write an essay on the main themes of Grapes of Wrath, you need to select one set of inter-related themes as a focus. Your thesis statement, which serves as a topic sentence for the first paragraph, should focus on the theme you choose and the main point you are trying to make. For example, you could start with “Grapes of Wrath is a story based on Biblical themes, and thus the major episodes in it can be read typologically, as twentieth century retellings of various Biblical stories.” Then you would focus the rest of your essay on biblical themes in the novel.
I want to focus my essay on the journey, so what themes go into that subject?