What favor does Chillingworth think he is doing for Dimmesdale?

In Chapter 9, Chillingworth becomes the "medical adviser"
to Dimmesdale.  This is an ironic relationship, of course, because the audience knows
(or will soon know) that the cause of Dimmesdale's failing health is in fact, his guilty
conscience.  Though Chillingworth does offer a variety of medical treatments for
Dimmesdale, the truth is that at the same time as he is treating Dimmesdale's
symptoms, he is feeding their
cause.

Chillingworth and Dimmesdale move in to the same
house and spend most of their time together.  From the very outset, Chillingworth has
correctly suspected Dimmesdale to be the father of Pearl.  These two educated men spend
most of their time engaged in scholarly debate, Dimmesdale from the side of a minister,
Chillingworth from a more secular side.  The one advantage Chillingworth of course has,
is that he knows Dimmesdale harbors a secret.  He does his best to hide this knowledge,
but at the same time, does what he can to be a constant reminder to Dimmesdale of his
sin and guilt.

Dimmesdale's physical health weakens as a
result, and Chillingworth takes care of him.  In this way, he is convincing himself that
this "favor" he is doing is for the minister's own
good.

Make no mistake.  Chillingworth's actions are simply
part of an evil and twisted revenge plot which victimizes Dimmesdale until the very end
of his life.