If Hester is guilty of the sin of adultery and roger chillingworth is guilty of the desire for revenge, what is reverend Arthur dimmesdale's...

In my opinion, Dimmesdale is guilty of two sins, the sin of pride and the sin of false witness (in addition to the sin of adultery).

I say this because Dimmesdale does not admit to the fact that he is Pearl's father and the man with whom Hester had the adulterous relationship.  When he does not admit to it, he is, in a way, bearing false witness.

He does this because he wants to keep his position as minister.  To me, that shows that he is proud -- he wants to maintain his position in the society even because it means something to him to have that position.