St. Thomas Aquinas defines law as such: “an ordination of reason for the common good from him who has care of the community, which is promulgated or made known” (ST I-II, Q. 90, a. 4).
Law, then, is nor primarily a mere set of rules or about control. Rather, law orders creatures to the ends for which God made them. For example, we cannot eat poisonous plants because doing so would be contrary to the our good – having life. However, law in itself tends toward the common good, rather than our individual goods. Therefore, even though my life is valuable by virtue that I am a human being, laying down my life for someone else would be a good action because it is oriented towards the common good. And, in most circumstances, doing what is best for oneself in accordance with charity will be the best for the whole society.
When our first parents were created, they did not have Original Sin, for God would not create beings who were compromised by evil. They had an intellect and a will and their lower powers were subjected to their higher powers, meaning their bodily inclinations were subjected to their spiritual ones. Yet, in rejecting God by stretching out their hands to sin, they lost this perfect subjection of body to soul, they lost their State of Grace. Consequently, they henceforth had difficulty resisting temptations to do things which their spiritual powers knew were wrong or bad for them. This tendency to sin, called concupiscence, meant that, left to their own devices, they would never find their way back to God.
But the Lord in His Infinite Mercy sent us His Only Begotten Son, so “that whoever believes in him should not perish but have eternal life” (Jn 3:16). In our fallen state, it is only by God’s constant gifts of grace, all of which flow from His Paschal Mystery, that we can follow the law. We need reason to follow the law, for the law is a rational ordering through which God, directly or indirectly, guides us to our proper end – eternal salvation.
But since our concupiscence often leads us to act contrary to right reason, we must constantly deny ourselves for God’s sake. This penance must last to our last moment if we want to persevere to the end in God’s Love and become those great saints He has called us to be. The law helps us to assume this penitential life and live it charitably. Without the law, we would have no guiding principle, nothing to light the way to Heaven.
Jesus Christ came “not to abolish [the law and the prophets] but to fulfill them” (Mt 5:17). In His Passion and Death, He “redeemed us from the curse of the law,” which we justly deserved because of our sins (Gal 3:13). He also gave us an example that the law is a means, not an end in itself. He, God, is the end, and the law is a means to get to Him.
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Types of Law
St. Thomas divides law into four categories: Eternal Law, Natural Law, Divine Law, Human Law.
Eternal Law is the pre-existing conception of reality in God’s mind. Since God’s essence is “To Be,” and thus His essence is existence, so His essence is His existence, for it is impossible to exist outside existence. God does not deliberate, but rather He sees and knows everything in an eternal gaze. Therefore, His Plan for the order of creation was planned from before all time and did not develop. The Eternal Law is thus the ordering of creation, which is eternal – it has always existed in God’s mind and always will.
Natural Law constitutes objects’ or creatures’ inclinations toward their proper end – participation in the Eternal Law. These participations take many forms, depending on what the object or creature is. Inanimate objects, non-sensory creatures, sensory creatures (animal), rational, sensory creatures (men and women), and purely rational creatures (angels) all orient themselves either consciously or unconsciously toward their end. For all creatures below humans, their end is physical death, so they orient themselves towards this life only. They also do not have an intellect, so they cannot know anything in the abstract, nor can they desire the good beyond what their bodies instinctively desire because they have no will. But men and angels, by their God-given intellects and wills, consciously choose either to follow the natural law or not to follow it. Additionally, we rational creatures have the Eternal Law impressed on our consciences, so that we intrinsically have some semblance of what pertains to our end – death and eternity – an can act in accordance with true humility and charity to choose the end for which we were made and for which God wants us to act (Heaven), lest we send ourselves to Hell.
Divine Law can be divided into Mosaic Law and the Law of the New Covenant consecrated in the Blood of Christ on the Cross. The Mosaic Law constitutes the precepts God gave to Israel. These precepts fall into three categories: the moral, ceremonial, and judicial precepts. The moral precepts distinguish right and wrong, the ceremonial precepts detail the liturgical and other practices of the Israelites, and the judicial precepts concern the human lawmaking and governing sphere of Israelite society. But while these precepts gave the Israelites knowledge of the truth, they did not give them the grace to effectively abide by those laws in their fullness. The New Law, according to St. Thomas, constitutes the grace of the Holy Spirit poured into our hearts. Christ’s Passion supersedes and makes obsolete the ceremonial and judicial precepts of the Mosaic Law, but He heightens and perfects the moral law: “You have heard that it was said to the men of old, ‘You shall not kill; and whoever kills shall be liable to judgment.’ But I say to you that every one who is angry with his brother shall be liable to judgment; whoever insults his brother shall be liable to the council, and whoever says, ‘You fool!’ shall be liable to the hell of fire” (Mt 5:21-22). With the New Covenant, God gives us the grace to follow the the Divine Law in all its fullness, both in faith and morals, but the demands are also greater. The greater the grace, the more is expected.
Human Law is the extension of the natural law in life. They are more particular applications of principles of the natural law. For example, a public sports field is open from 6:00am to 10:00pm. There is nothing intrinsically wrong from using the field between 10pm and 6am, but to ensure the public’s safety and to clean the field and give the grass some rest (for example), human lawmakers have decided to enforce the period from 10pm to 6am as times when one cannot use the field. These laws carry weight and ought to be obeyed because they are applications of at least what the lawmakers think (at least in theory) pertains to the good in view of one’s final end. However, if a manmade law is sinful, meaning it violates the natural law, and thus the eternal and divine laws, it must be disobeyed, for to obey it would be to disobey the higher law. Therefore, it is really no law at all, but sin, which is an act of evil, which is the absence of the good, and thus of any ordering to the good.