Third Question: On the Mutability of Eternal Law

St. Thomas, I-II, q. 93, a. 2.

243. Eternal law in itself is immutable, but its knowledge in us is mutable. Eternal law, because it is the essence of God, cannot be known in itself except by God and by the blessed; but all rational creatures are able to know it according to a certain greater or lesser irradiation of it. For every knowledge of truth is an irradiation and participation of divine truth and therefore of eternal law; but all know truth in some way, more or less, at least as to the common principles of natural law, and therefore also eternal law.

Hence although eternal law in itself is immutable, nevertheless its knowledge can be increased or diminished in individuals, according as they know more or less the other laws which are its participation, as will be said below.