In Act One of The Crucible, what is the heart of the disagreement between Reverend Parris and John Proctor?

Beyond the fact that Reverend Parris and John Proctor don't like each other, Parris feels that Proctor leads a faction to remove him from his position, and Proctor feels that Parris preaches too much fire and brimstone and isn't a godly man.

Parris feels that everyone must be perfectly obedient to the church (and, by extension, himself) "or the church will burn like Hell is burning," he says.  Of course, when everyone is obedient, it...

Beyond the fact that Reverend Parris and John Proctor don't like each other, Parris feels that Proctor leads a faction to remove him from his position, and Proctor feels that Parris preaches too much fire and brimstone and isn't a godly man.

Parris feels that everyone must be perfectly obedient to the church (and, by extension, himself) "or the church will burn like Hell is burning," he says.  Of course, when everyone is obedient, it makes his job a lot easier.  He claims that "There is a party in this church.  I am not blind; there is a faction and a party."  He believes that a secret group, led by Proctor, is working to get rid of him.  His pride is wounded by the meagerness of his salary in his eyes, and he feels that he is persecuted in the town so that if he every proposes anything, "there by a howling riot of argument."  He feels ganged up on, unappreciated, and powerless to effect change.

Proctor, meanwhile, rarely comes to church because, as he says,

I have trouble enough without I come five mile to hear him preach only hellfire and bloody damnation.  Take it to heart, Mr. Parris.  There are many others who stay away from church these days because you hardly ever mention God any more.

Proctor feels that Parris only preaches fire and brimstone, and the minister seems not to say anything uplifting or comforting.  Proctor's got enough to worry about without coming all the way to town to hear doom and gloom at church.  It also bothers Proctor that Parris, unlike any minister before him in Salem, demanded the deed to his house (a house that only ever temporarily belongs to the current minister).  Proctor seems to feel that Parris is being greedy; Parris feels it would be a "mark of confidence" in him.   

Proctor does seem to bait Parris, and Parris allows Proctor to get his goat every time.  When Parris insists that there's a party in the church that works against him, Proctor jokes with Giles Corey, "Let's find the party.  He says there's a party."  Their antagonism of one another will continue, almost to the end of the play.