What Purpose is the Law?

The apostle Paul has labored long and hard in this letter to attempt to persuade the churches of Galatia that salvation does not come through the law or the works of the law. Here in Chapter 3 alone, he mentions that the Spirit is not received through the works of the law, and there is actually a curse upon everyone who is trying to be saved by the works of the law. He has said that no one can be justified by the law in the sight of God, for the just shall live by faith. He has tried to show them in every way that the law is not of faith.
Now the question that should naturally arise in our minds, is this: What purpose does the law serve then? Since it was God who gave the law, then why did He give it? Well, there are a number of reasons that God gave the law, but these verses show 3 of the most important reasons why God gave it. 1st – It was added because of transgressions. 2nd – It was added as a covenant which would be a shadow of the good things to come when Christ the promised Seed arrived. And 3rd – It was given to show us that the ultimate Mediator between God and man must be the God-Man, not Moses.