Convinced that Dimmesdale is Pearl's father, Chillingworth embarks on a campaign to make his patient as miserable as possible. Dimmesdale continues to suffer greatly and comes to hate Chillingworth for mistreating him.
The two secret sinners, Chillingworth and Dimmesdale, become lost in a vicious cycle of suspicion and hatred.
Dimmesdale continues to preach and delivers some of his most passionate sermons, which focus mostly on the topic of sin. He describes himself as a "pollution and a lie" to his parishioners, yet he does not confess and they continue to view him favorably.
Dimmesdale's sin lets him empathize with other sinners. The Puritans, though they are so concerned with sin, can't recognize a sinner.
Dimmesdale's guilt makes him hate himself. He punishes himself physically and emotionally, staying up nights thinking about confessing, and starving and whipping himself. His health crumbles, as does his sense of self. As the narrator observes, "To the untrue man, the whole universe is false." Yet the chapter ends with the suggestion that Dimmesdale has come up with a plan that might help him ease his suffering.
Dimmesdale's secrets reduce his identity to a shadow of doubt and self-hate. His secrets, kept to protect his public reputation, have made him internally "untrue." By this point it's obvious that relief can only come from confession of his sin.