Tommy: You ask a very broad question when you’re asking about the Law, but I’ll take a stab at making it simple.

Preaching of the Law can fall under any or all of three major categories: Curb, Mirror, or Guide.

The Law as a Curb: Within the life of every person—before and after the fall—the Law serves the same function. It exists as a curb, telling us what is right and what is sinful. In other words, it directs us in the way we should go. God’s “Law” told Adam and Eve that it was wrong to eat of the fruit of the Tree of the Knowledge of Good and Evil. In this sense, the Law keeps us from sin (or at least it should).

The Law as a Mirror: Since we live after the fall, we know that sin is passed down to us as our inheritance, and apart from the Gospel we are all damned. In this context, the Law serves as a Mirror in which we see our filthy reflection as compared to God’s perfection. It is through this that the Holy Spirit convicts our hearts and shows us our need for a Savior. The Law “kills” us so that the Holy Spirit, may raise us up by His grace through imparted faith and imputed righteousness. Again, though this may seem to be a bad thing, especially at the point when we realize how damned we are. Some people (like Judas Iscariot) can never get past this conviction of the Law, and it leads to despair. In some, however (like Peter), it leads to repentance, faith, and trust in Christ. The Law is good.

The Law as a Guide: After we “get saved”, we are not free from the Law. We are freed from sin, unto good works. Whereas before we believe, even our good works are like filthy rags, when we come to faith, our righteous acts are now… good works. We live a life of gratitude towards Christ for His free gift of salvation. Now, here’s the kicker… in the life of a Christian, even this third use of the Law can mimic the first or the second use. A believer who is tempted may look to the Law as a curb on his behavior. When he gives into the temptation, the Law, as a mirror, shows him that his behavior is not befitting of one who lives under God’s grace and drives us again to repentance. But these are just functions of the Law as a Guide in the life of a believer. Still, the Law is good.

Wow… how much more Lutheran can I sound?

One more thing about the word “Law”... Most of the times you see the word “Law” in the Old Testament (cf. Psalm 19:7 and all of Psalm 119, when it’s not referred to as word, commands, or precepts), the Hebrew word is actually “Torah”, which has a connotation of teaching or handed down instruction/wisdom and even a tone of grace, not a harsh edict of “Follow this or else…”. This makes all the difference in the world. The reason it is rendered in English the way it is, is because the scholars who wrote the Greek translation of the OT (the Septuagint) translated it as nomos, which is the Greek word for Law. No doubt, the Torah does have laws and commands in them, but as Romans 7 says, the Law is good.

It is unfortunate that one of God’s greatest acts of grace (the recorded Old Testament) is seen by many to have a tone of condemnation.

Perhaps this is a bit much, but hopefully it helps.