I think that the first reason Proctor's criticism of Parris is significant is because it brings how the latter's hypocrisy. Proctor's fundamental claim is that Parris does not bring honor to the church because he is so concerned with his material status and representation within it. This is important because a society like Salem that placed so much weight in the power of religious leaders was being questioned in Proctor's criticism. Additionally, Proctor being critical of Parris is important because it helps to feed Parris' own desire to name Proctor as part of the town's hysterical reaction to witches and witchcraft. At several points in the drama, it is clear that Parris wishes to turn the lens of social critique and judgment on Proctor because of his own criticisms of the Reverend. In this, one can see how the witch trials were more an exercise of power than anything else. At the same time, I would suggest that Proctor being critical of Parris helps to evoke a major element of his characterization that ends up helping to define him in the drama in terms of refusing to be silent in the face of authority. Proctor does not let the authority of Parris silence him. This is something seen at the end of the drama in Proctor's declaration of his name.