|St. Augustine of Hippo, 354-430 AD|
So by putting both sides--He hath mercy o whom He will have mercy, and whom He will hardeneth--we are given to understand that the new statement agrees with the former one, viz., the hardening which God causes is an unwillingness to be merciful. We must not think that anything is imposed by God whereby a man is made worse, but only that he provides nothing whereby a man is made better. But if there be no distinction of merits, who would not break out into the objection which the apostle brings against himself? "Whou wilt say then unto me, Why doth he still find fault? For who withstandeth his will?" God often finds fault with men because the will not believe and live righteously, as is apparent from many passages of Scripture. Hence faithful people who do the will of God are said to walk blamelessly, because Scripture finds no fault with them. But he says, "Why does he find fault? Who withstandeth his will" through "he hath mercy on whom he will and whom he will hardeneth." Let us look at what was said above and let it direct our interpretation as the Lord himself gives us aid.
~ To Simplician–On Various Questions, Chapter 15