Why can't Chillingworth be impartial in Chapter 10

Chillingworth seems to cross the line in this chapter from having human motives to suffering inhuman possession. Indeed, although the narrator proceeded no further than calling Chillingworth “evil” in motives and in deed, now Chillingworth's soul is attacked, and he is even compared to Satan, a thief of men's souls. Chillingworth can't be impartial because he is consumed by his own vendetta against Dimmesdale and the people he feels wronged by.