Chillingworth knows that Dimmesdale is a sinner, yet a reputable man of faith, and that the silent pursuit of him will destroy him from the inside out. Not to mention, Chillingworth has a personal vendetta against Dimmsdale for performing an act with the woman Chillingworth thought was his very own. Vengence can move people to do terrible things to each other. Chillingworth respectfully helps maintain Dimmesdale's anonymity from the crime that he participated in with Hester, but it is almost as if helping prevent the truth from coming out only further hurts Dimmesdale. This personal attack gives Chillingworth purpose and a false sense of satisfaction since he can't seem to get it from having a wife who loves him. His promised wife, Hester Prynne, seems to have already consumated with a man (Dimmesdale), and is therefore now impure and less desirable. At least the pursuit of the man who destroyed her gives Chillingworth some value and purpose.