In The Scarlet Letter, what happens to Pearl, what does she do, and what changes her from chapters 17-24?

In the forest, late in the story, Pearl is deeply affected by the sight of her mother with Reverend Dimmesdale in the forest. As Hester and Dimmesdale talk and eventually plan to leave Boston together (with Pearl, of course), Hester unclasps the scarlet letter “A” from her breast and tosses it away. When she then calls on Pearl to come join them, Pearl is hesitant. After a while, Pearl’s reticence rankles her mother. Finally, Pearl points toward her mother, who realizes that the problem is that the scarlet letter is missing.

“I see what ails the child,” whispered Hester to the clergyman, and turning pale in spite of a strong effort to conceal her trouble and annoyance. “Children will not abide any, the slightest, change in the accustomed aspect of things that are daily before their eyes.”

Pearl is unable to relate to her mother without the scarlet letter on her breast—it’s been there for Pearl’s entire life. Symbolically, this represents the idea that Pearl can only accept her mother as she really is, which includes her sinful nature. It is not possible for Hester to change who she is and keep her daughter’s love and acceptance. Hester finally retrieves the letter and puts it back on, at which point Pearl joins them. However, she is unwilling to accept Dimmesdale, and when he kisses her she runs to the brook and washes the kiss away. This act sets up Pearl’s change of heart later in the story.

In the novel’s next-to-last chapter, Dimmesdale finally succumbs to his guilt and confesses his part in Hester’s adultery. As the trio stands before the community at the scaffold, Pearl shows her acceptance of Dimmesdale, now that he has publicly joined her and her mother:

Pearl kissed his lips. A spell was broken. The great scene of grief, in which the wild infant bore a part, had developed all her sympathies; and as her tears fell upon her father’s cheek, they were the pledge that she would grow up amid human joy and sorrow, nor forever do battle with the world, but be a woman in it. Towards her mother, too, Pearl’s errand as a messenger of anguish was all fulfilled.

What ultimately changed Pearl was Dimmesdale’s dying confession—his admission that he was Hester’s lover and Pearl’s father. This acceptance puts Pearl squarely in the world as a legitimate person, one who is no longer at odds with her mother and society in general.