When societies or governments create lots of laws, it’s often a sign that something is going wrong with that particular society. St. Thomas Aquinas tells us, the original and proper use of the law is to help people live virtuously. It is to encourage their basic goodness, and to help them live together in harmony.
The basis of all Gospel teaching about law is that there is the eternal law of God, and the natural law within humans, which shares in the eternal. The summary of the natural law for us humans is the Ten Commandments. They are reminders of the best part and highest aspirations of the natural human law that lives within all of us. Given that we are fallen creatures, we sometimes forget how to live in harmony with each other and with God. The Ten Commandments remind us of how to do this. At one time in history God gave a more complex and detailed law to the children of Israel, called the Law of Moses. This law added many observances and rules about purity and religion. Again, this was to help the people live holy lives in a world dominated by idolatry. As St. Paul says, this law was like a schoolteacher, which led the people to God. With Jesus, God has come to us, and the Law of Moses is no longer necessary. This is the argument that Jesus is having with the Pharisees. They are saying that the Law of Moses should still be observed. Jesus is saying that the natural law, as reflected in the Ten Commandments, is, and always has been, the most important.
In reality, then, there is a good aspect to the whole idea of law. God creates the universe and everything in it. Each thing has its own nature and way of behaving. Humans have their specific way of being, which includes sharing the life of God. This way of being is summed up by the Ten Commandments, and the person of Jesus and the gift of the Spirit bring all the commandments to perfection. Jesus came to complete the law. We can apply this to our lives in two main ways. Firstly, we can deepen our understanding of the Ten Commandments and the teaching of the Church about our human nature. Secondly, we can participate responsibly in whatever society we live in. It is part of our responsibility as Christians to try to ensure that the laws of the land are designed to help us all live virtuously, according to our human nature, and not according to false ideas of our human nature.