The highest goal of humans is to become just people, by submitting to natural law (nomos) as an expression of the Divine Mind (logos). State laws are obeyed because they are in accordance with natural law. Even Stoic thinkers argue that human society is maintained and developed because of obedience to natural law.

Natural Law Doctrine of the Middle Ages

St. Thomas Aquinas was the greatest philosopher of the Scholastic school in the Middle Ages. He accepted the influence of Aristotle but expressed it with Christian religious dogma so that it formed a separate system of thought. Thomas Aquinas formulates law as "a regulation originating from reason for the common good made by someone who has an obligation to protect his society and enact it". Because the world is governed by the Divine order, the entire world community is governed by divine reason. Divine law is the highest. Thomas Aquinas distinguishes four types of law, namely: lex aeterna, lex naturalis, lex divina and lex humana.

Lex aeterna is divine reason that guides all movements and actions in the universe. Only a small part of the lex aeterna can be captured by humans through the mind that God has given them. The part that can be captured is called lex naturalis, which provides direction to human activities through general instructions. The most basic instruction is that good must be done, while evil must be avoided.

Regarding what is called good, Thomas Aquinas associates it with what is a natural tendency in humans. First, is the natural human instinct to maintain his life. Second, the attraction between the two sexes and the desire to raise and educate children. Third, humans have a natural desire to know God and a tendency to reject ignorance. Fourth, humans want to live in society and therefore it is natural for humans to avoid actions that harm the people who live with them. Meanwhile, lex divina is what is contained in the holy books and lex humana is what is contained in the new and old covenants.

Thus, the doctrine of natural law according to Thomas Aquinas is none other than part of God's law, the part that is expressed in the mind of nature. Humans as rational beings, apply this part of God's law to human life, therefore they can distinguish between good and bad. This comes from the principles of eternal law, as expressed in natural law, which is the source of all human laws.