The following text is from an email Pastor Phelps sent to his elders:
I hope I didn't cause confusion by a point I tried to make about our intended uses of the Law and how the Law's accusing power is never silenced. I hope to clarify this further. Thinking in terms of the three uses - curb (outward restraint of sin), mirror (showing us our sin and our need for the Cross), and guide (showing us how we should live as Christians), I have two assumptions: 1) all three uses are always inherent in the Law itself - these potentialities are embedded in all of God's commandments; 2) the Holy Spirit is sovereign in how He may amplify one, two or all three uses to the hearer - even if our intended use is different.
I thought I'd share an illustration of this:
Imagine a man in our congregation who is seriously contemplating adultery with a woman at his work. They have spent inordinate time together, and he is getting signals that she is attracted to him. He has begun to fantasize about committing adultery with her, and to plan a way to be alone with her.
At worship, he hears the Seventh Commandment expounded. The preacher intends the "mirror" use, to show us our sin & our need for Christ. As the man hears and is convicted about the spiritual dangers of heart adultery, the wrath he deserves for it, and how he needs to repent and claim the forgiveness Christ won for him (mirror), the Spirit also uses the Law to outwardly curb his temptation to commit adultery. He resolves that he can no longer spend the kind of time he has been with this woman. He thinks about the trouble he would have brought on himself, his family, this woman, and his workplace. He is also convicted about how unfaithful his heart has been towards his wife - how he must delight in her alone emotionally and sexually, and view her as a good gift from God. The Holy Spirit thus guides him into how he should live as a Christian husband, out of gratitude for Christ's mercy to him as a sinner.
The point is, the Holy Spirit uses the Law to curb, convict, and guide according to His own sovereign purposes. This has a few implications in my mind.
1) We can and should accent the particular uses of the Law in our preaching and teaching - but always bearing in mind the Spirit's sovereignty and the inherent convicting power of the Law;
2) The imperatives of the Law (including NT imperatives) should always be grounded in the Gospel, because we cannot presume to isolate the Law as "guide" from the Law as "mirror";
3) Even if only the "mirror" use is the focus of a homily or sermon, the guidance of the Law (third use) is implied, and may well be amplified by the Holy Spirit;
4) Since the ultimate purpose of Christian preaching is to preach Christ and Him crucified for us, and since the Word of grace is the means by which the Christian is sanctified and the Church is edified, and since the ultimate goal of that proclamation is to present every man perfect in Christ, Christ and His Gospel should never be assumed but should be the main thrust and predominate accent of every sermon.