This question is a matter of debate over at Ref21, with Rick Phillips taking the pro side, and Paul Levy taking the con side. I have to say, having read many expository commentaries, that I whole-heartedly agree with Rick. Paul raises some important points, however, which deserve careful consideration.
The first point he raises is that “it is remarkable how many of these sermons are very similar and how they even sometimes cite each other.” It is true that I have seen expository commentaries cite each other. However, the very same point could be raised against more technical exegetical works. Indeed, I have seen many times a certain helpful quotation from someone like Westcott quoted in about ten more recent commentaries, none of them expository. Commenting on Scripture is an inherently accumulative discipline. That is, one accumulates insights from the best of church history. There is bound to be repetition. But there will also be nuggets that are gained in the twelfth or even twentieth commentary that were not present in the first or second. Furthermore, if some of the sermons are similar, then shouldn’t that be an encouragement to the preacher that if his sermon winds up looking a bit like those, that he is in good company, and is not spouting off heresy? While we certainly wish to discourage plagiarism, originality is not always a virtue!
Secondly, he is not convinced that all sermons should be turned into books. This appears to be a more general point that he fleshes out in his points about the difference between preaching and reading, and the fact that not all sermons are great. I agree that not all sermons should be turned into books. Of course, when one considers how many Reformed and Presbyterian preachers there are out there (to take but a small segment of the Christian Church), the vast majority of preached sermons never make it to print. There are well over a thousand sermons preached every single Sabbath day just in the Reformed and Presbyterian community. I would be shocked if more than five of them wind up getting published. That being said, his implied caution to hot-shot preachers who think they’re pretty good is well-taken: don’t automatically assume you are the exception! Every preacher is tempted by the thought that their words are pure gold, and that everyone should hang on their every utterance.
The point about the difference between preaching and reading is a valid one. I am not necessarily in favor of always editing sermons for publication by taking out the specific applications to a particular congregation (unless, of course, specific names are mentioned). One of the problems that preachers typically have is making applications specific enough. I know that I have this problem. It is all too easy to make an application hang out in the realms of generality without ever giving a concrete example, or bringing it home to people in a sharp way. If the sermons are written already with a view to publication, do they have this problem, or do they get edited with this problem in view? Of course, there is also a corresponding danger: if preachers are making their sermons ready for publication before they are even preached, they can often sound like lectures, in the sense that there is not enough repetition and glue holding the message together in a unity. The repetition and glue is not so necessary in a print form. Still, these points do not mean that the difficulties are insurmountable.
Lastly, he wants preachers to read the great books and the classics. A hearty amen from me on that. I don’t, however, see why reading the classics and the greats has to exclude reading expository commentaries in preparation for preaching on that passage. A pastor should read widely, and in many fields. To see how preachers have handled the passage in the past can sometimes even be a life-saver on particularly difficult passages, where the exegetical works might give no help at all.