Law and Grace
Well, perhaps we should define these terms before using them. The law is what God has commanded us to do, and what He has forbidden us to do. There is more than one kind of law. In the Bible, you have ceremonial law, moral law, and civil law. The ceremonial law is given mostly in the book of Leviticus. It is concerned with the worship of God, and the sacrifices. I believe that all the ceremonial law pointed to Christ, and that Christ was its fulfillment. Therefore, since it is fulfilled, we no longer observe it. The moral law, as the catechism says, is summarily comprehended in the Ten Commandments. The moral law is the following: "The Lord our God the Lord is one. You shall love the Lord your God with all your heart, and with all your soul, and with all your strength, and with all your mind. You shall love your neighbor as yourself." The first of these, to love God with your whole being, is expanded into the first four of the Ten Commandments. The second of these, to love your neighbor as yourself, is expanded into the last six of the Ten Commandments. It is this law that is in question in most people's minds these days. Should we obey the Ten Commandments? Finally, the civil law contains rules like "You shall not boil a young kid in its mother's milk." Also, rules such as the establishment of cities of refuge in the Old Testament. I believe that the civil laws should in general take their form from the Ten Commandments. That's a qualified statement, so before you accuse me of being a theonomist, it might be better to clarify with me.
Grace is a gift from God when we deserve the opposite. I like the following illustration. Suppose someone hires me to wash their car for $10. I wash the car, and I get the $10. I have received a wage: it was what I deserved. Now suppose I did nothing, and still got the $10. Then I got mercy. But now suppose I took a sledgehammer and smashed the car to smithereens. And I still got the $10. That is grace.
So now that we have defined law, and more particularly the moral law, let me ask the question again: what is the role of the moral law (from now on in this post, law means the moral law) in the world? Well, the Reformers had a three-fold answer to that question. The first use of the law is to restrain evil. The law, they argued, was imprinted on every person, and thus their conscience led them to be not as bad as they could possibly be. The second use of the law is to convict a man of his sin. Sin is defined as any want of conformity unto, or transgression of the law of God. The word literally means, "to miss the mark." So sin is doing what God forbids, or failing to do what God requires. More on this second use of the law later on. The third use of the law is as a guide to Christian living. The Christian is to follow the law.
So let's ignore the first use of the law for now, and concentrate on the second and third. Here's what I believe happens. A man is unregenerated by the Holy Spirit. Then someone comes to him and gives him the law. He is convicted of his sin, and by regeneration of the Holy Spirit, he is enabled to accept Jesus Christ as his personal savior. It is by grace that this man is saved. It is a gift from God, not by works lest he should boast. But now this mans is saved from sin and to good works. In other words, he must now follow the law. In my post entitled The Meaning of Life, I explained why loving God and obeying Him are precisely the same things. It is important to realize that even though he must obey the law, such obedience has nothing to do with his conversion. God didn't save him on the basis of what this man had done. Rather, God saved him on the basis of what Christ had done. But now, this man is trying to live according to the law, because he knows that's the right thing to do. He still will not have the strength to do it on his own; he needs God's strength. In other words, more grace. So here's the pattern: law-grace-law-grace. They work together, in perfect harmony. Both are essential for salvation. Law tells us something about what salvation is, and grace actually saves us.
I mentioned earlier about the second use of the law. Here is where the law actually helps me in my sanctification (the process started when you are saved and continuing until you die). The law, through the Holy Spirit, convicts me of my sin. Now this, I believe, is one of the surest signs of my salvation. It is assurance of salvation. I can know that I am saved, because the Holy Spirit keeps bringing me back.
I hope I've answered the question: what has law to do with grace, to some extent. I'd welcome comments.