Why does Mr. Linder visit the apartment

Karl Lindner comes to the Younger apartment to convince them to sell the house they've purchased in Clybourne Park.

Explanation:

The Younger family receives money from their father's death. Their mother uses some of it to put a down payment on a home in Clybourne Park; it's a safer neighborhood and predominately white. The Younger family is black.

When Mr. Lindner arrives, he introduces himself as a representative of the Clybourne Park Improvement Association. He says the purpose of the organization is to do upkeep and special projects. There's also a New Neighbors Orientation Committee; he says they see people who move in and let them know the way they do things in Clybourne Park. Mr. Lindner is the chairman of that committee.

He says that he believes that black people are happier living in their own communities. The Clybourne Park association wants to purchase the home they've bought from them. He assures them that it will come with a profit to the Younger family. Ultimately, they don't take the offer and they prepare to move to Clybourne Park.