John Steinbeck is important for several reasons.
The first reason Steinbeck is important is his documentation of several crucial elements of American life and culture. He wrote about the plight of migrant workers, poor farmers, and others who lived economically marginal lives. He wrote about the Great Depression so powerfully that his works still shape American understanding of this national trauma.
However, the most important reason Steinbeck is important is the quality of his writing. He’s considered great. His writing is realistic, contains articulate political analysis, applies and examines powerful symbols, and, most important of all, is emotionally moving and beautiful.
You can see the importance and quality of his work in the fact that Steinbeck won a Pulitzer Prize for The Grapes of Wrath, and a Nobel Prize for his body of work.