Objection 1. It would seem that not all human affairs are subject to the eternal law. For the Apostle says (Galatians 5:18): "If you are led by the spirit you are not under the law." But the righteous who are the sons of God by adoption, are led by the spirit of God, according to Romans 8:14: "Whosoever are led by the spirit of God, they are the sons of God." Therefore not all men are under the eternal law.
Objection 2. Further, the Apostle says (Romans 8:7): "The prudence [Vulgate: 'wisdom'] of the flesh is an enemy to God: for it is not subject to the law of God." But many are those in whom the prudence of the flesh dominates. Therefore all men are not subject to the eternal law which is the law of God.
Objection 3. Further, Augustine says (De Lib. Arb. i, 6) that "the eternal law is that by which the wicked deserve misery, the good, a life of blessedness." But those who are already blessed, and those who are already lost, are not in the state of merit. Therefore they are not under the eternal law.
On the contrary, Augustine says (De Civ. Dei xix, 12): "Nothing evades the laws of the most high Creator and Governor, for by Him the peace of the universe is administered."
I answer that, There are two ways in which a thing is subject to the eternal law, as explained above (Article 5): first, by partaking of the eternal law by way of knowledge; secondly, by way of action and passion, i.e. by partaking of the eternal law by way of an inward motive principle: and in this second way, irrational creatures are subject to the eternal law, as stated above (Article 5). But since the rational nature, together with that which it has in common with all creatures, has something proper to itself inasmuch as it is rational, consequently it is subject to the eternal law in both ways; because while each rational creature has some knowledge of the eternal law, as stated above (Article 2), it also has a natural inclination to that which is in harmony with the eternal law; for "we are naturally adapted to the recipients of virtue" (Ethic. ii, 1).
Both ways, however, are imperfect, and to a certain extent destroyed, in the wicked; because in them the natural inclination to virtue is corrupted by vicious habits, and, moreover, the natural knowledge of good is darkened by passions and habits of sin. But in the good both ways are found more perfect: because in them, besides the natural knowledge of good, there is the added knowledge of faith and wisdom; and again, besides the natural inclination to good, there is the added motive of grace and virtue.
Accordingly, the good are perfectly subject to the eternal law, as always acting according to it: whereas the wicked are subject to the eternal law, imperfectly as to their actions, indeed, since both their knowledge of good, and their inclination thereto, are imperfect; but this imperfection on the part of action is supplied on the part of passion, in so far as they suffer what the eternal law decrees concerning them, according as they fail to act in harmony with that law. Hence Augustine says (De Lib. Arb. i, 15): "I esteem that the righteous act according to the eternal law; and (De Catech. Rud. xviii): Out of the just misery of the souls which deserted Him, God knew how to furnish the inferior parts of His creation with most suitable laws."
Reply to Objection 1. This saying of the Apostle may be understood in two ways. First, so that a man is said to be under the law, through being pinned down thereby, against his will, as by a load. Hence, on the same passage a gloss says that "he is under the law, who refrains from evil deeds, through fear of punishment threatened by the law, and not from love of virtue." In this way the spiritual man is not under the law, because he fulfils the law willingly, through charity which is poured into his heart by the Holy Ghost. Secondly, it can be understood as meaning that the works of a man, who is led by the Holy Ghost, are the works of the Holy Ghost rather than his own. Therefore, since the Holy Ghost is not under the law, as neither is the Son, as stated above (4, ad 2); it follows that such works, in so far as they are of the Holy Ghost, are not under the law. The Apostle witnesses to this when he says (2 Corinthians 3:17): "Where the Spirit of the Lord is, there is liberty."
Reply to Objection 2. The prudence of the flesh cannot be subject to the law of God as regards action; since it inclines to actions contrary to the Divine law: yet it is subject to the law of God, as regards passion; since it deserves to suffer punishment according to the law of Divine justice. Nevertheless in no man does the prudence of the flesh dominate so far as to destroy the whole good of his nature: and consequently there remains in man the inclination to act in accordance with the eternal law. For we have seen above (Question 85, Article 2) that sin does not destroy entirely the good of nature.
Reply to Objection 3. A thing is maintained in the end and moved towards the end by one and the same cause: thus gravity which makes a heavy body rest in the lower place is also the cause of its being moved thither. We therefore reply that as it is according to the eternal law that some deserve happiness, others unhappiness, so is it by the eternal law that some are maintained in a happy state, others in an unhappy state. Accordingly both the blessed and the damned are under the eternal law.
Source: Summa Theologica (New Advent)