What is the theme of A Raisin in the Sun ?

There is no singular theme in A Raisin in the Sun; however, there does seem to be an overriding theme: the collusion of race and socio-economic class as barriers that impede social mobility.

The impeding of socio-economic mobility is what causes dreams to be "deferred"-- as Langston Hughes writes in his poem alluded to in Hansberry's title--to dry up like "a raisin in the sun." This idea is symbolized by the plant that Lena Younger has in the one window in the front rooms; it struggles to sustain itself on this small amount of sun.

After Mrs. Lena Younger receives the $10,000 life insurance check for her deceased husband, she dreams of moving to a house with a yard where she can have a garden. Her son Walter Lee dreams of owning a business and of being the new man of the family. Ruth, his wife, also anticipates a new home and new beginning as she has been depressed by Walter's dissatisfaction and a pregnancy they cannot afford. Beneatha is the daughter of Lena, a young woman who is uncertain of her future as she waivers in her choice of values and boyfriends.

Unfortunately, Walter's dream of owning a liquor store is shattered when a friend to whom he has given a part of the insurance money runs off with it. Also, Lena's dream of owning a home starts to fall through when objections come from the suburban homeowners' association. But, when Mr. Lindner visits the Youngers and offers more than the family has paid for the house, Walter Lee changes his mind about accepting the money. He tells Mr. Lindner,

WALTER: [W]e have decided to move into our house because my father—my father—he earned it for us brick by brick. We don’t want to make no trouble for nobody or fight no causes, and we will try to be good neighbors. And that’s all we got to say about that. We don’t want your money.

Walter has changed his priorities from becoming prosperous to the welfare of his family. Lena closes her eyes and nods as though she were in church. But Walter has been "saved" in the sense that he now is the man of the family, and Youngers will no longer have their dreams dry up like "raisins in the sun."