Summary: God's promise of salvation through faith far exceeds any promise the Old Testament law could give.
THE SUPERIORITY OF GOD'S PROMISE
We have many laws in our country. Laws are important for any given society. On the early mining frontier, many towns sprang up around strike areas. These were often terrible places to visit or live. For a long time, there were no laws there. Crime was rampant. Vigilante groups finally arose to give some semblance of law and order. Laws also keep order in our society. Without them, there would be chaos. For those who choose to break them, punishment awaits. This is the deterrent so that they might obey. Yet it is impossible to legislate morality. We can have all the laws we like, but we can never make people moral. The fact that we have laws does not keep people from breaking them. The rise in criminal activity is proof of that. That is a choice they have to make. In fact, only God can create in people the desire to be more than they normally are. The flip side is that we are promised not to be punished if we obey the law.
Paul has appealed to the experience of the Galatians to prove to them that faith is the way and only way to have a relationship with God. If this was not enough, he appealed to the example of Abraham, father of the faithful. He proved from Scripture that God accepted Abraham because he believed his promise. He reminded them that all who tried to live under the law were under a curse because one would have to perfectly obey the law and this they could never do. The obvious question that would now follow is what was the purpose of the law. If the law could not make one right with God, why did God give it?
Paul also probably anticipated another question from the Judaizers. True, God accepted Abraham by faith, but when he gave the law to Moses the way of salvation changed. Obedience to the law was now the way of salvation. Abraham and others who lived before the law were saved by faith because they did not have the law.
In these verses, Paul answers this imaginary argument. He shows that the covenant God made with Abraham was unconditional. God based it on his faithfulness to the people whereas the covenant with Moses was based on the people's faithfulness to God. They would be unfaithful, but God would remain faithful. Thus the Mosaic covenant was conditional while the covenant with Abraham was unconditional. The promise made by God to Abraham was superior to the one made with Moses.
Now the law had a purpose. It was to demonstrate to people that they were totally sinful. It showed people that they did not have the ability to obey God. They would miss the mark every time. There was a need for mercy and grace. The law could never provide this. It was obedience or else. Only the promise of God could bring mercy and grace. The law was designed to drive people to a desperate state of guilt. Paul will later say of the law that it was a “tutor to lead us to Christ, that we may be justified by faith.” The law would show a person that their living was more than just wrong. It was a sin against God.