The Lutheran Confessions answered this question when it was brought up by a theologian named Agricola. In the Epitome of the Formula of Concord, Article VI, the Lutheran church confesses:
"The preaching of the law is to be diligently applied not only to unbelievers...but also to people who are genuinely believing, truly converted, regenerated, and justified through faith. For although they are indeed reborn and have been renewed in the spirit of their mind, such regeneration and renewal is incomplete in this world. In fact, it has only begun, and in the spirit of their mind the believers are in a constant war against their flesh (that is, their corrupt nature and kind), which clings to them until death. On account of this...it is necessary for the law of God constantly to light their way lest in their merely human devotion they undertake self-decreed and self-chosen acts of serving God."The same question continues to come up today, thanks to many teachers who avoid proclaiming the Law because “the goodness of God leads to repentance” (Romans 2:4). Such preachers really do not preach the “good news” either. Instead, their hearers receive advice on how to live their lives and help themselves, which is really Law after all.
This picture illustrates the reason that even Christians need to hear the Law preached. Consider these two, equally true statements by the apostle Paul:
“For the love of Christ compels us, because we judge thus: that if One died for all, then all died; and He died for all, that those who live should live no longer for themselves, but for Him who died for them and rose again. Therefore, from now on, we regard no one according to the flesh… Therefore, if anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new” (2 Corinthians 5:13-17).And yet, on the other hand:
“I know that in me (that is, in my flesh) nothing good dwells; for to will is present with me, but how to perform what is good I do not find…For I delight in the law of God according to the inward man. But I see another law in my members, warring against the law of my mind, and bringing me into captivity to the law of sin which is in my members” (Romans 7:18, 22-23).This means that all Christians – even Paul – are like the face in this picture. The sinful nature is still there, battling against the “new creature” that God has created in us through faith in Jesus Christ (Ephesians 2:10). To borrow a phrase from ancient Christian teachers, we are “at the same time saints and sinners.”
We are completely justified by God’s grace, for Jesus’ sake; yet we are also completely sinful. We are newborn children of God, destined to be perfected in heaven. But during this life, the battle continues between the “old Adam” and the “new man” in us, through Christ (see Ephesians 4:16-18; Philippians 3:8-14).
So we need to hear both the Law (such as the 10 Commandments), and the Gospel (“good news”). We still need God’s Word to call us to repentance, because we are still sinners. But all our hope is in the “good news” of forgiveness and salvation. By this free gift of God, we are “renewed in the spirit of (our) mind,” and we daily “put on the new man which was created according to God, in true righteousness and holiness” (Ephesians 4:23-24).
Also, we eagerly look forward to the day of resurrection, when our corrupt bodies will be transformed into perfect, sinless bodies. Again, Paul writes:
“Behold, I tell you a mystery: We shall not all sleep, but we shall all be changed—in a moment, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, and the dead will be raised incorruptible, and we shall be changed… So when this corruptible has put on incorruption, and this mortal has put on immortality, then shall be brought to pass the saying that is written: ‘Death is swallowed up in victory’…The sting of death is sin, and the strength of sin is the law. But thanks be to God, who gives us the victory through our Lord Jesus Christ” (1 Corinthians 15:51-52, 54, 56-57).IMAGE: actor Adam Baldwin in a still from Francis Ford Coppola's film Dr. Jekyll & Mr. Hyde.