What is the meaning behind the quotation, "I’ve heard you to be a sensible man, Mr. Hale. I hope you will leave some of it in Salem" in The Crucible?

John Proctor hopes Reverend Hale's arrival will end the hysteria about witches, but it doesn't because things have progressed too far.
This comment is about the witch trials causing mayhem in Salem. The hysteria over witches is unreasonable. Reverend Hale is supposed to be an expert. The witch trials are a "beloved errand" for him. Proctor hopes Hale can end the girls' accusations of witchcraft on innocent people.
John Proctor certainly does not believe in witches.

Giles Corey: He don’t believe in witches.
Proctor, to Hale: I never spoke on witches one way or the other. Will you come, Giles?
Giles: No — no, John, I think not. I have some few queer questions of my own to ask this fellow.

The witch trials are a result of a group of girls who claim to have been attacked by witches, who in reality are just townspeople. Since the town fears witches, they believe the girls. The girls' ringleader is Abigail Williams, who has a specific reason to get back at John Proctor because he spurned her after they had an affair.
When Hale arrives, he brings with him his expertise and a bunch of books.

Parris, delighted: Mr. Hale! Oh! it’s good to see you again!Taking some books: My, they’re heavy!Hale, setting down his books: They must be; they are weighted with authority.

For a group of supposedly God-fearing people, the people of Salem go from normal to crazy pretty quickly. Hale, the supposed expert on witches, is unable to derail the insanity. By the time the trials are over, many innocent people will have died as a result of them.