To be reasonable protects truth and results in right order. To be unreasonable denies truth and results in chaos. Stated another way, law emanates from practical reason. Eternal law is that law which emanates from God's eternal conscience and practical reason. It is the basis for all other laws.
Natural law is an expression of eternal law.
It is given by God to creation, particularly to those creatures that enjoy free will and the use of reason. It is the law within each person that moves us to grace and gives inclination to salvation. Divine positive law is that law expressly given by God in commandments. Human law, both ecclesiastical and secular, are proper expressions of Divine law. We are created in the image and likeness of God.