How does Lorraine Hansberry make the pages 91, 92, 93, 94 and 95 (Act 2, scene 1) so significant?

In the last part of Act 2, Scene 1, Mama announces that she has bought a house and that they will move on the first of the month. Just before she enters, Walter and Ruth are arguing, worrying, and commiserating about the problems they are facing. Walter has his heart set on using his father’s insurance money—although the money rightly belongs to his mother—to open a liquor store.
Hansberry heightens the effect by having Mama slowly build up to the fact that the house is in a white neighborhood. Mama finally reveals this by telling them first the neighborhood and then the exact street address. Ruth and Walter are stunned. Walter is initially speechless while Ruth puts both their feelings into words.

MAMA (Frightened at this telling) Well—well—it’s out there in Clybourne Park—
(RUTH’S radiance fades abruptly, and WALTER finally turns slowly to face his mother with incredulity and hostility)
RUTH Where?
MAMA (Matter-of-factly) Four o six Clybourne Street, Clybourne Park.
RUTH Clybourne Park? Mama, there ain’t no colored people living in Clybourne Park.
MAMA (Almost idiotically) Well, I guess there’s going to be some now.

While Mama has seemed the most conventional character in the play, almost a stereotype of the long-suffering, supportive Black mother figure, she turns out to be the person who has taken the boldest move, in making her whole family the wedge that will integrate the neighborhood.
Ruth immediately comes around and crows her jubilation at this change, addressing the apartment itself:

All I can say is—if this is my time in life—MY TIME—to say good-bye …to these goddamned cracking walls!... then I say it loud and good, HALLELUJAH! AND GOOD-BYE MISERY… I DONT NEVER WANT TO SEE YOUR UGLY FACE AGAIN!

Walter cannot hide his anger, and after Ruth exits speaks rudely and disrespectfully to his mother, who tries to explain why her decision is best for the family. Accusing her of butchering his dream, he storms out.
https://www.penguinrandomhouse.com/books/74861/a-raisin-in-the-sun-by-lorraine-hansberry/9780679755333/