Explaining the Errors of Preachers and When to Warn Against Them

Question:
Does explaining the errors of preachers mean warning against them? And when is a person warned against?

Answer:
First, errors must be known and defined, because many people today have come to say that anyone who disagrees with them is wrong and not on the right path. Errors are those that contradict the Book and the Sunnah. So whoever contradicts the Book and the Sunnah has erred. But if someone contradicts the custom of people or what some people are upon, then it is looked into to see if the contradiction agrees with what came in the Book and the Sunnah or not. The standard is the Book and the Sunnah, with preachers and with others. The standard by which error is known from truth, right from wrong, and guidance from misguidance is the Book and the Sunnah. So whoever contradicts the Book and the Sunnah has erred, and whoever agrees with the Book and the Sunnah is correct. This is justice.
So if a preacher has errors that contradict the Book and the Sunnah, then he must be advised, and this matter must be made clear to him. If he complies, praise be to Allah. If he does not comply, then it is said to the people, and it is made clear to the people, that this preacher has erred, and he has erred in such and such, and that he refused to accept, he refused to accept the advice. So that people may be aware of his state.