Thomas Aquinas discusses the relationship between human nature and law in the second part of his Summa Theologica. Let’s look at some of what he has to say, according to the questions identified, so that you can better understand human nature, law, and the relationship between them.
Questions 57–58 discuss the intellectual virtues and their difference from the moral virtues. Human beings are called to develop habits of virtue, both intellectual and moral, so that they can know reality and respond to it appropriately. In question 58, Aquinas says that “Human virtue is a habit perfecting man in view of his good deeds.” These habits can be intellectual or moral, and the two work together.
But according to Aquinas, human beings are fallen and sinful, and therefore they need laws to help them develop virtue. See questions 90–96 for the discussion of law. Aquinas spends many questions exploring the subject of law, talking about what it is and how it works. Law, he says, is intended to make people good and to guide them toward virtue (see question 92). Law comes in many forms: eternal law, natural law, human law, and divine law. Eternal law and natural law are known to all people and apply to all people. They are pre-programmed, so to speak, and can never be abolished. Human law is supposed to conform to eternal and natural law. Divine law is what God gives people to direct their conduct. It is revealed and often clarifies and adds to natural law, for sinful human beings, in Aquinas’s view, need more explicit instructions.
Note that according to Aquinas, God’s law is perfectly in tune with human nature, for God created human beings and understands them better than they understand themselves. He knows the laws that people need to grow in virtue.