An expository sermon or lesson is one that…allows the biblical text to supply both the shape and the content of the message or lesson from that text itself. The reason for this limitation is important. It is all too easy to fall into the trap of pouring what we already know of the grace of God into the different containers made up of different verses of Scripture without seriously giving each text an opportunity to first teach us what it wants to say. Not only does such preaching become repetitive, but it severely handicaps the preacher’s opportunity to grow and stretch in new areas.
—Walter C. Kaiser Jr., Preaching and Teaching from the Old Testament, pp. 49-50