The medieval canon lawyers placed the natural law in divine revelation as testified to in the two Testaments of Scripture. Thomas Aquinas, while not denying the position of the canonists, placed the natural law in creation itself. Aquinas distinguishes between the divine law found in Holy Scripture, and the natural law found in creation. This distinction is an important one. By placing the natural law in Scripture, its reach is limited to a particular time and place. However, if the natural law is placed within creation itself, this particular imprint of God on the human person is and has been available to the whole human race in every age.
Note, then, that whereas for the canonists the Scriptures are the first location of the natural law, for Thomas, of course, without denying the ultimate origin of the ius naturale in God, the order of nature has been distinguished from revelation, and, so far as we are concerned, is the first locus of the natural law. We might say that the canonists’ conception was more dominantly theological or undifferentiated, and in this sense we can see that Thomas’s view allows for a universe in which a natural order has sufficient integrity to be read by man without immediate recourse to revelation.
Far from unlinking natural law from the God of revelation, however, Thomas’s distinction between divine law and the natural law brings to full articulation an idea that had long been developing, namely that the path to holiness revealed in Scripture is not a positivistic decree only fideists can accept, but has a purchase on the inner rational structure of human nature. Thomas’s account of the relation between natural and divine law, it seems to me, reveals its deepest meaning when read against the background of his doctrine, rediscovered in our day by Henri de Lubac, that nature, as such, desires a fullness that it can attain only within the context of gracious elevation to the visio beatifica.
— Glenn W. Olsen, “Natural Law: The First Grace,” Communio XXXV (Fall 2008)