From Pope St. John Paul II’s encyclical Veritatis Splendor (1993):
The alleged conflict between freedom and nature also has repercussions on the interpretation of certain specific aspects of the natural law, especially its universality and immutability. “Where then are these rules written”, Saint Augustine wondered, “except in the book of that light which is called truth? From thence every just law is transcribed and transferred to the heart of the man who works justice, not by wandering but by being, as it were, impressed upon it, just as the image from the ring passes over to the wax, and yet does not leave the ring”.92
Precisely because of this “truth” the natural law involves universality. Inasmuch as it is inscribed in the rational nature of the person, it makes itself felt to all beings endowed with reason and living in history. In order to perfect himself in his specific order, the person must do good and avoid evil, be concerned for the transmission and preservation of life, refine and develop the riches of the material world, cultivate social life, seek truth, practise good and contemplate beauty.93
The separation which some have posited between the freedom of individuals and the nature which all have in common, as it emerges from certain philosophical theories which are highly influential in present-day culture, obscures the perception of the universality of the moral law on the part of reason. But inasmuch as the natural law expresses the dignity of the human person and lays the foundation for his fundamental rights and duties, it is universal in its precepts and its authority extends to all mankind. This universality does not ignore the individuality of human beings, nor is it opposed to the absolute uniqueness of each person. On the contrary, it embraces at its root each of the person’s free acts, which are meant to bear witness to the universality of the true good. By submitting to the common law, our acts build up the true communion of persons and, by God’s grace, practise charity, “which binds everything together in perfect harmony” (Col 3:14). When on the contrary they disregard the law, or even are merely ignorant of it, whether culpably or not, our acts damage the communion of persons, to the detriment of each.
92 De Trinitate, XIV, 15, 21: Corpus Christianorum, Latin series 50/A, 451.
93 Cf. Saint Thomas Aquinas, Summa Theologiae, I-II, q. 94, a.2.
— Veritatis Splendor 51