Consider the Langston Hughes poem (reprinted in the beginning of the book) from which the book draws its title. How does it foreshadow the issues in the play? How does the play answer the questions posed in the poem?

The words of Langston Hughes's poem "A Dream Deferred" foreshadow the struggles of the Younger family and their dreams, along with the disappointments that the family also faces. The poem also foreshadows the power of love and respect to keep dreams from being deferred, as well the capability of the Youngers to pursue their dreams. 
As the family awaits the life insurance check for the deceased Mr. Younger, the mother and her children consider what dreams to pursue with this money. Mrs. Younger recalls how she and Big Walter moved into the place that they are now living: "We wasn't planning on living here no more than a year." They hoped to purchase a home in Morgan Park; in fact, they had picked out the place. Mrs. Younger adds the following:

"You should know all the dreams I had 'bout buying that house and fixing it up and making me a little garden in the back. . . . And didn't none of it happen" (Act I). 

If Mrs. Younger has this new dream of a home deferred, then it too will "dry up like a raisin in the sun."
Walter, who is a chauffeur, longs to be his own boss. He wants to invest some of the insurance money in a liquor store which he feels can bring him financial freedom. His sister Beneatha hopes to go to college and become a doctor. By doing this, she can break through gender and racial barriers.
When Mrs. Younger receives the $10,000 insurance check, she uses part of this check to make a down payment on a house in Clybourne Park because she has watched her family "sag like a heavy load." (Walter's wife Ruth thinks of having an abortion since she and Walter cannot afford another child, and Beneatha and Walter argue constantly.) Mrs. Younger realizes that Ruth's dreams are beginning "to stink like rotten meat" and her troubles "sag like a heavy load." Further, Mama (Mrs. Younger) explains why she has made the down payment on a new house:

"I just seen my family falling apart today. . . . We was going backwards 'stead of forward—talking 'bout killing babies and wishing each other was dead . . . when it gets like that in life, you just got to do something different, push on and do something bigger" (Act II).

Mrs. Younger buys the new house to hold her family together and give them hope. However, when Walter learns that his mother plans to finance Beneatha's education, he is very disappointed that he cannot purchase a liquor store which he believes will fulfill his dream of financial success and independence. In his despair, Walter drives around town and spends his nights brooding in a local bar. Realizing that Walter's "dream deferred" has begun to "fester like a sore," Mama gives her son the remainder of the money but asks that he put aside some for Beneatha's education. Unfortunately, Walter entrusts a friend named Willy with the money to purchase the store. Instead of investing the $6500.00 for Walter and himself, the man absconds with it. Walter's lost dream now "explodes." An enraged Beneatha bemoans the following: 

While I was sleeping in that bed in there, people went out and took the future right out of my hands and nobody asked me . . . they just went out and changed my life (Act III).

To compensate for this loss of the money which his mother has trusted him to use wisely, Walter decides to accept the offer from Mr. Linder of the homeowners' association to buy back at a financial gain the house Mama has purchased. But, when Mr. Linder arrives and pulls out the papers, Walter notices that his son Travis watches and listens. Ashamed of his surrender to the prejudices of the community, Walter changes his mind and refuses to take the money and deny his mother her long-awaited dream. He cannot let Mama's dream "sag, like a heavy load."
Right before they depart their old apartment, the family gives Mama gardening tools and a large hat to wear as she works in the garden at the house of her long-awaited dream.