The Enchiridion

Then shall be made clear much that is now dark. For example, when of two infants, whose cases seem in all respects alike, one by the mercy of God chosen to Himself, and the other is by His justice abandoned (wherein the one who is chosen may recognize what was of justice due to himself, had not mercy intervened); why, of these two, the one should have been chosen rather than the other, is to us an insoluble problem. And again, why miracles were not wrought in the presence of men who would have repented at the working of the miracles, while they were wrought in the presence of others who, it was known, would not repent.

For our Lord says most distinctly: “Woe unto you, Chorazin! Woe unto you, Bethsaida! For if the mighty works, which were done in you, had been done in Tyre and Sidon, they would have repented long ago in sackcloth and ashes.” And assuredly there was no injustice in God's not willing that they should be saved, though they could have been saved had He so willed it. Then shall be seen in the clearest light of wisdom what with the pious is now a faith, though it is not yet a matter of certain knowledge, how sure, how unchangeable, and how effectual is the will of God; how many things He can do which He does not will to do, though willing nothing which He cannot perform; and how true is the song of the psalmist, “But our God is in the heavens; He has done whatsoever He has pleased.” And this certainly is not true, if God has ever willed anything that He has not performed; and, still worse, if it was the will of man that hindered the Omnipotent from doing what He pleased.

Nothing, therefore, happens but by the will of the Omnipotent, He either permitting it to be done, or Himself doing it.