31 Now why were the eyes of Moses made to shine because of the glory which he saw, while on the contrary [the eyes of] Paul, instead of being made to shine, were made utterly blind? Yet we may be sure that the eyes of Moses were not stronger than those of Paul; for they were akin in one brotherhood of blood and flesh. But another power through grace sustained the eyes of Moses; whereas no power was added in mercy to the eyes of Paul, beyond their natural power, which in wrath was taken from them. But if we say that their natural power was taken away from them, and that [it was] on this account he was defeated and overcome by the overpowering light—for had their natural power remained, they would have been able to endure that supernatural light. Yet let us be sure of this, that as often as anything transcendent is revealed, that surpasses and transcends our nature, our natural power is not able to stand before it. But if on the other hand another power beyond our natural one is added to us, then by that power received by us in excess of and beyond nature, we shall be able to stand before any strange thing which comes upon us supernaturally.
Source: On Our Lord (New Advent)