Why has Proctor set himself against Parris?
Proctor has set himself against Parris because he does not like Parris. When Parris comes to town, he demands things that the previous men in his position did not demand.
This aspect of his personality is evident in his dispute about whether the provision of his firewood should be taken out of his salary or is extra to it.
He insists that respect be shown to him by the townspeople in material ways. This is not merely a request from Parris, but a demand. Given from the pulpit, these kinds of demands mark the church experience for people like Proctor.
Proctor concludes from this behavior that Parris is using his official position inappropriately for his own gain. Self-interest is at the heart of Parris' character and Proctor sees this trait accurately.
Proctor’s conflict with Parris stems from what he sees to be the minister’s hypocrisy of wanting more than his due.
This type of hypocrisy is a betrayal of the community, when seen in the light of Proctor's view. Importantly, this view of Parris robs the reverend of his moral authority.