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."