How had Chillingworth changed through the years?

After devoting seven years to the torture of another human soul, Chillingworth had become a devil of sorts,

"in a word, old Roger Chillingworth was a striking evidence of man’s faculty of transforming himself into a Devil, if he will only, for a reasonable space of time, undertake a Devil’s office."

Chillingworth derived pleasure from his torture of Dimmesdale and he became old and pathetic. Even Hester feels sorry for this wretched man. When Hester looks at the doctor he asks her what she sees. Hester replies, “Something that would make me weep, if there were any tears bitter enough for it”