In Galatians 3:18-20 Paul turns from denouncing the law as a means of salvation to talk about what the law actually is. The law is good. God gave us the law to serve all mankind. I live in my house, not because I’m 
stronger than my neighbor, but because law has given it to me. In a world without law we have no peace, no security, no free pursuit of happiness. The law establishes boundaries for all of us. The law served to restrain sin. Here’s what Paul said, “For if the inheritance comes by the law, it no longer comes by promise; but God gave it to Abraham by a promise. Why then the law? It was added because of transgressions, until the offspring should come to whom the promise had been made, and it was put in place through angels by an intermediary. Now an intermediary implies more than one, but God is one.”
The first function of the law is to help stay, hinder, suppress, and reduce sin. We are all sinners and if left to ourselves it would become like the days of Noah. We would be killing and stealing and cheating one another. Law gives us restraint. Whenever I see a state trooper on the highway I look at my speed? Don’t you? The law was designed to restrain our fallen human natures. Gromacki writes, “If no restrictions were ever placed on unregenerate wills, then sinners would manifest their position in every conceivable evil practice. The intent of the law, therefore, was to reduce the amount of sin that could be committed.” Paul also tells us in Romans to obey the law because God ordained its representatives. God gave us law so we could live peaceful, godly lives. Law is still good because there are still sinners in the world.
Notice the comment that it was “ordained through angels.” Acts 7:53 says the same thing! If you remember the mediation of the law to Israel from Sinai everyone was afraid and ran. It underscores the fearfulness of the law! Hustable says in the Pulpit Commentary, “The whole passage is tinctured with the feeling that the giving of the law, as contrasted with the dispensation of the Messiah, was marked by distance, sternness, and alienation.” The people (Exodus 20:19-21) demanded Moses to serve as their mediator. That shows their great anxiety concerning the law. Obviously, the law does not bring peace and joy but great fear. However the Gospel of Christ, which is received by faith, brings great peace and joy. This restraining power of the law is only needed when the depraved nature of man dominates. When the “seed” shall come, Christ, He will redeem us from slavery to the law and put His law in our hearts. This clearly lets us know that God’s intent from the beginning was that the law be a temporary remedy for the sinfulness of man, it was never intended to be the cure. But when Christ came, He came to give sight to the blind and to bring healing to the sick. In Christ the restraining function of the law is unnecessary!