I’ve heard many sermons in my day that made important, truthful, relevant points from the text of Scripture but that I would still say fell short of actually preaching the text.
What I mean is that the text was the starting point or the jumping off point for thoughts that, as truthful, relevant, and necessary as they were, had little relation to what the text was actually saying. I don’t think that Paul, or Peter, or John, or Luke would have recognized the logical connection between these points and the text.
Mark Dever has defined expository preaching as preaching where the main point of the text is the main point of the message. (See Nine Marks of a Healthy Church, p. 40-42.)
These sermons I’ve mentioned failed to do this. These same sermons could have been preached from the writings of a philosopher, or from a novel, or from an episode of a television program, or a movie, or a joke, or anything because they were really a loosely connected collection of thoughts.
I note that these types of sermons never seem to have a big idea or main point or homiletical proposition or whatever you call the theme that binds the sermon together and brings it to its logical conclusion. I don’t think this is a coincidence.
The proposition (as I was taught to call it years ago) is supposed to be driven by what the text is actually saying. The main theme of the text leads us in our development of the big idea or proposition which in turn drives the rest of the sermon.
This ensures that our sermon is not a disjointed collection of thoughts (remember, a sermon is a rifle not a shotgun) but it also keeps us true to the meaning of the text.
This has the added benefit of helping us transition between the movements of the sermon by connecting the point back to the main point and also lets us repeat the main point several times which in turn impresses the main point of the sermon (and the text!) upon the hearers. When they read that text later they won’t remember all the details, but if you’ve repeated that big idea several times during the sermon they will remember that and they will be able to recall more than they would have otherwise.
So spend some of your sermon preparation thinking about the main point of the text and then “Keep the main thing the main thing” so that when you’re done you are confident that you’ve actually preached the text and haven’t simply preached from the text.