Among the four or five dialogues I had with J. Ligon Duncan at the Pastor’s Conference, one of them was extremely significant. Earlier Dr. Duncan spoke on Expository Preaching from the Old Testament. It was certainly a pertinent topic in light of the almost overwhelming Baptist audience, who tend to overlook the relevance of the Older Covenant. He listed ways to preach the Old Testament. His last point is the one I wish to bring to our attention: Preach the Christian Life in the Old Testament. As an example of this, Ligon reminded the audience of Luke 17 where the author urges the reader to “Remember Lot’s wife”. In that example, she is used not merely as a Redemptive Historical figure, but as a physical representation of how we ought not to behave. In Duncan’s words, those who avoid using the Bible in order to affect our behavior are denying the very writers of Holy Writ. Simply because there have been abuses in preaching–which leads to legalism and moralism– does not mean that we ought not to stress it where it is stressed in the text.
John Frame’s criticism of this form of thinking is worth reading:
I have heard Christians say that our goal in preaching should be only to spread the word, not to bring conversion, since that is God’s work. The result is often a kind of preaching that covers biblical content, but unbiblically fails to plead with sinners to repent and believe. 
It is here where Frame’s language is helpful. He divides the Bible into two emphases: Indicative and Imperative. The “Indicative” refers to what happens in redemptive history (Salvation’s history or the unfolding of the ages), whereas the “Imperative” refers to the obligation or responsibility of the Christian under God’s authority. When the Bible is preached and does not challenge in any way our behavior, we are disobeying apostolic instruction. Further, the opposite is also dangerous. When the preaching is merely concerned about changing behavior, the message becomes moralistic and meritorious in nature. The Scriptures bring these two together in an unending bond. Paul himself brought both together in Colossians 3:1-3: You have been raised (Indicative)…so set your hearts on things above (Imperative). The Scriptures demand both.
 Luke 17:32
 In this case, we ought not to disobey God’s Word. There is a strong ethical component here, not an abstract mention.
 Frame, John. The Doctrine of God, Footnote, pg. 123.
As Reformed folk I think that we generally go along with that view of preaching that holds that it is the primary means that God uses to convert the soul. I don’t think that this is a one-time event, and I think that you can bear that up by connecting some of the dots in Calvin:
-Calvin posits an identity between regeneration and repentance in his Institutes.
-Calvin does not think of repentance as an event, nor does he think of it as the idetification of particular sins (which he seems to find a Romish practice). Instead, it is a turning of the whole life toward God, which seems to happen over the whole life of the believer.
-Calvin sees good works as evidencing conversion. Effectively, they are the yield of a heart right with God.
It may not be an elegant way of doing it, but I think that if one goes with Calvin here, preaching about what ‘repentant life’ looks like is part and parcel with preaching repentance.
Along with Dr. Duncan, I note that there are some passages where you can’t do more than read the Scriptures if you are going to self-proscribe prescriptive preaching. Jeremiah Burroughs preached for at least seven weeks on the implications of the passage in Philippians that speaks of living a life worthy of the Gospel. With a self-proscription he wuld have had to simply read the verse and go on.
I agree Tom. At the Conference i saw a copy of a Purtian book with 217 messages on galatians 5:17…Flesh vs. spirit.
If you haven’t read Bryan Chapell’s book on Christ-centered preaching, you might find it interesting. The section on the “deadly be’s” addresses the trap of moralistic preaching–the tendency of many preachers to tell their hearers to “be like Moses,” or “be like David,” without reminding them of Paul’s admonition–“follow me as I follow Christ.” The life lessons of the OT saints are indeed valuable, as long as we keep in mind that it is no longer we who live, but Christ who lives in us.
Although I speak as one who has never preached, Duncan’s point seems impressively reinforced by the two best-documented sermons that I recall from the New Testament: Peter’s at Pentecost and Stephen’s before the Sanhedrin. I cannot think of two more perfect homiletic marriages of the indicative and the imperative than these two examples. And how different were the responses! We all have the Pharisee in us and need to be challenged on a weekly basis. This being so, I heartily agree with Tom that repentance and conversion are progressive activities and demand the proclamation-application of the Word for the enrichment of grace.
Those are great references. I could really multiply the amount of verses that beautiful display that marriage as you stated. This is a historic moment. I actually found Ligon compelling and even agreed with him. This is rare indeed.