The characters change both physically and mentally. Part of Hawthorne's theme relates to the connection between emotion and appearance, as is best viewed in Dimmesdale and Chillingworth. But lets backtrack.
Hester - changes the least. In the second chapter, she is described as having much beauty and a bit of faint heart. Hawthorne describes her long flowing hair and youthful appearance. She trembles on the gallows and fears the townspeople. However, as time passes, the plain clothing she chooses to wear subdues her appearance. She is never described as old, but as plain, as part of the surroundings. She has accepted her world. Only in the forest does she break free of it. SHe has accepted her fate as well, and becomes calm adn collected around the townspeople and the townsleader, accepting the growing role they provide to her.
Dimmesdale, though initially described as youthful, attractive, and energetic, grows slowly older and weaker. His body thins, his shoulders become stooped, his voice falters when he speaks, and he is prone to illness. As his guilt overwhelms him, his body weighs him down and despite one moment after his visit to the forest, he stays weighed down until the moment of his confession and death.
Chillingworth's body is also corrupted by his internal conflict. Though already old, Hawthorne describes him as increasingly gnarled, gaunt, and harsh in appearance. He looks more demonic with each passing day, as his need for vengeneace consumes. His eyes glow with a fiery and malevolent desire as he closes in on his prey, and he changes from the angry, calm man he was in his prison visit with Hester to the obsessed and irrational man determined to exact the most public revenge possible.
Pearl experiences the most positive change. While the deceit perpetrated by her parents lives, she is described by Hawthorne as bordering on the supernatural. She is elf-like, ostracized by the townspeople, and a mystery to her mother. Upon Dimmesdale's confession, however, Hawthorne immediately describes the peaceful and forgiving change that takes over her face. The epilogue lets us know that she went on to lead, not only a successful life, but a life in which she is embraced by society. Quite different from troubled youth!
Hester Prynne experiences the greatest change. In shame she accepts her fate; in knowledge and maturity she discards the appellation of "Adultress."
For example, in Ch. 3 "The Recognition" one of the townspeople remarks on her punishment: "A wise sentence! This will be a living sermon against sin until the ignominious letter be engraved on her tombstone!"...She (Hester) fled for refuge...". But by Ch. 18, "A Flood of Sunshine", Hester has rejected injustice: "So speaking, she undid the clasp that fasted the scarlet letter, and, taking it from her bosom, threw it to a distance among the withered leaves."Hester is not the only character to experience radical change. So too does Reverend Dimmsdale. Though he thinks he is intelligent and a moral "light", Hawthorne frequently depicts him in the dark, a device with a pretty straightforwrd metaphor. However, Dimmesdale finally comes to understand just how clueless he is. By Ch 14, "Hester and the Physician," Dimmesdale begins to realize how limited his knowledge is: "All my life has be made up of earnest, studious, thought, quiet years, bestowed faithfully in my own knowledge." What Dimmesdale has come to understand is that it is a moral failure to withhold knowledge.
Only one character remains constant in his lack of development: Chillingsworth. He is evil from beginning to end. Hawthorne describes the villain from the outset as being "shady"; he is constantly "in the shadows" (Ch 3, "The Recognition") and described often by Pearl as "the black (evil) man" in the middle (Ch 9, "The Leech"). By the conclusion, "there was no more Devil's work to do on this earth for him."