I have written before about staying within a low fence and generally sticking in the passage you are in for the message. However, there is a similar but slightly different temptation we face as preachers. It is the temptation to preach the whole book in which the text is found and fail to fully preach the text itself.
Why is this a temptation? It doesn’t happen every time. But if you are preaching a single message rather than a whole series (either as part of a series where others are preaching too, or as a stand-alone message), then you are more likely to face this temptation. It comes from studying the passage in its context, the very thing you should be doing. It comes from enjoying the study of the whole book, seeing the flow of thought perhaps clearer than you have before. It comes from an understanding on your part that this text makes so much more sense once the context is fully understood.
What is the problem? Well, you have to decide. Should you preach the whole book, or should you preach the specific preaching text. If it is part of a series, do not neglect your specific text. If it is a stand-alone, you have the option of preaching the broader text (but if you do, remember that the message must be evident in the text sitting on listeners’ laps, whichever parts you point them to look at, or your message will apparently lack biblical authority). The problem comes when you try to preach a specific text, but spend so much time giving the context and flow of the book that you fail to adequately explain the text that is read to the listeners.
So what to do? Once a decision is made on whether you are preaching the main idea of the whole book, or the specific passage, check your outline/notes/manuscript. Does the message content reflect your objective? Be careful not to over-introduce. It is painful, but cut unnecessary introduction and context. Give enough to set up the preaching text, but be sure to preach the text itself.