The source of my authority in this pulpit is not...my wisdom; nor is it a private revelation granted to me beyond the revelation of Scripture. My words have authority only insofar as they are the repetition, unfolding and proper application of the words of Scripture. I have authority only when I stand under authority. And our corporate symbol of that truth is the sound of your Bibles opening to the text. My deep conviction about preaching is that a pastor must show the people that what he is saying was already said or implied in the Bible. If it cannot be shown it has no special authority.
John Piper