I think, like TDOL said, it has to do with having the power to persuade. In your example of a preacher, this could be taken offensively, because the preacher does not feel a need to persuade. Rather, they are interpreting and relaying what is already known to be fact (as far as the church is concerned). A salesman, or someone in debate, or even a business negotiator might take this as a compliment, where their goal is to persuade. I think it depends a lot on the intonation of your voice, also. I apologize in advance if that's hard to follow!

Jessica