But the former aspect of an intellectual and studious man, calm and quiet, which was what she best remembered in him, had altogether vanished, and been succeeded by a eager, searching, almost fierce, yet carefully guarded look. It seemed to be his wish and purpose to mask this expression with a smile, but the latter played him false, and flickered over his visage so derisively that the spectator could see his blackness all the better for it.
In Chapter 14 of The Scarlett Letter Hester seeks a conference with Chillingworth while they are both in a field at the seaside, which is where Hester bids Pearl go to play while she talks with Chillingworth, "yonder gatherer of herbs." Hester is surprised by her first close look at Chillingworth in seven years' time, for his appearance has changed. As the quote above indicates, he no longer looks like a quiet, contemplative scholar pursuing intellectual activity. He now has a strange look to his face that it seems to Hester he is trying to disguise by a smile. The new look that is "eager, searching, almost fierce" was only heightened by the attempt to mask it with a smile. Hawthorne uses this description to reinforce the labors Chillingworth has, first, put into discovering the identity of Pearl's father and, then, put into deviously tormenting Dimmesdale.
Further, Hester notices a red fire in his eyes that seems to emanate from a fire "smouldering...within his breast." This symbolic representation of a fire in his breast aligns him symbolically with both Hester and Dimmesdale. [Perhaps Hawthorne is suggesting that he bore part of the blame for Hester's shame, as it is clear he bears part of the blame for Dimmesdale's suffering.] The narrator sums up Hester's perceptions by stating that Chillingworth's seven years of searching out tortuous thoughts had been turning him "into a devil." Hester also perceived that his ruin came as another price of the adultery between herself and Dimmesdale.
Hester's perception of Chillingworth is expressed in her final plea to him, which is that he cease spreading torture, "for the hatred that has transformed a wise and just man to a fiend," and seek instead to forgive and stop spreading evil so that he, the one who was wronged, might find the good and peace, "There might be good for thee, and thee alone, since thou hast been deeply wronged."