Over at Expository Thoughts, Matt Waymeyer has a great quote from Jay Adams on the use/misuse of commentaries in preaching:
Speaking of exegesis, how do you do it? Do you cobble together bits and pieces from various commentaries into some explanation of the preaching portion? Or do you do the hard work of figuring out for yourself what the passage says, using various commentaries to help you? Between these two approaches to the text, there is a large difference. That for which you have worked will come through in your preaching as authentic. That which has been cribbed from some commentator who did the work, will come through as inauthentic (unless, of course, you are an astute actor). Hard work requires using a goodly number of sources to help you come to valid decisions about a passage. But it doesn’t mean abusing them by mere copying. Are you guilty of this sin, preacher? If so, repent, and begin to do the right thing that you know, down deep, you ought to be doing. Rightly handling the Word of God is not only work, but a great responsibility.
My philosophy has been…do all the hard work of digging & interpreting; but when you are done, check two or three “good” commentaries to see what they say. I have commented here before that there have been times when I was going a specific direction in interpreting a passage, but when I read the commentaries saw that I had missed the direction totally! While that is a frustrating waste of time, it is better to find it out BEFORE you preach it than after!
More often than that, however, the commentaries generally shed light on something I didn’t see. I think that referencing them is critical, but as Adam says, “it doesn’t mean abusing them by mere copying.