Karl Lindner's visit in Lorraine Hansberry's A Raisin in the Sun is one of the most significant episodes in the play, for it brings the theme of racial prejudice into the Youngers' living room and provides the test through which the family's dignity is finally proved.
Who Lindner is and what he wants. Lindner is the representative of the Clybourne Park Improvement Association, the welcoming committee of the all-white neighbourhood into which the Youngers plan to move. Behind his polite manner lies a request that the family should not move in; the association even offers to buy the house back at a profit. His visit exposes the reality of housing segregation and the polite face of racism.
Significance as a revelation of racism. Lindner shows that the Youngers' struggle is not only against poverty but against a society that would deny a black family the right to live where it chooses. His offer makes the theme of racial discrimination concrete and personal.
Significance as a test of character. The visit becomes a moral trial, especially for Walter. After the insurance money is lost to Willy Harris, Walter is tempted to accept Lindner's money to recover the family's fortunes. The decision forces the family to weigh dignity against desperation.
The climactic refusal. When Lindner returns, Walter, standing before his son Travis, refuses the offer and declares that the family will move into their house because his father earned it. This is the emotional climax of the play. Lindner's visit thus becomes the occasion for Walter's coming into manhood and for the family's collective assertion of pride.
In conclusion, Lindner's visit is significant because it dramatises the racism the Youngers face, tests their integrity at the moment of greatest weakness, and provides the platform for their triumphant assertion of human dignity.