Galatians 3:21-22

Is the law, therefore, opposed to the promises of God? Absolutely not! For if a law had been given that could impart life, then righteousness would certainly have come by the law.

(v21, NIV)

Paul has been going on for a while about how we are justified by faith. Paul is speaking against a group of people who believe that it is by the law that one is justified. Now that he's made his case and numerous points for why it is not by the law but by faith that we are justified, Paul looks to deal with another point they may bring up. Since faith is being painted in such a great light in contrast to the law, and since Paul just made the argument about the promises of God, they may wonder if the law is contrary to the promises. Paul makes it clear that they are not. Paul begins with a hypothetical situation. If the law was given to us so that the law could give us life, then righteousness would be by the law. However, we already know because of the case Paul made earlier that we are justified by faith and not by the law. So even though this situation Paul pants is untrue, he paints it for a reason.

But the Scripture declares that the whole world is a prisoner of sin, so that what was promised, being given through faith in Jesus Christ, might be given to those who believe.

(v22, NIV)

The picture Paul painted in the last verse was meant to be contrasted with this verse. The scripture itself reveals that life does not come by the law. Instead of a life giving law, it is an imprisoning law. However, this law still has a purpose. It imprisoned us to sin so that the promise would be given in faith to Jesus. And through Jesus those who believe might benefit. The law has a purpose. The law was given by God and so was the promise. They both are from God and they both have a purpose or purposes.