As you start preparing your sermon you must begin with the exposition of your passage or single verse...all preaching must be expository. You do not start with a thought, even though it be a right thought, a good thought; you do not start with that, and then work out an address on that. You must not do that, because, if you do, you will find that you will be repeating yourself endlessly...So you must be expository; and in any case my whole argument is that is should be clear to people that what we are saying is something that comes from the Bible. We are presenting the Bible and its message.
Martyn Lloyd-Jones, Preaching & Preachers