Nicene and Post-Nicene Fathers: Series I/Volume V/On Rebuke and Grace/Chapter 31

Chapter 31.—The First Man Had Received the Grace Necessary for His Perseverance, But Its Exercise Was Left in His Free Choice.

The first man had not that grace by which he should never will to be evil; but assuredly he had that in which if he willed to abide he would never be evil, and without which, moreover, he could not by free will be good, but which, nevertheless, by free will he could forsake. God, therefore, did not will even him to be without His grace, which He left in his free will; because free will is sufficient for evil, but is too little for good, unless it is aided by Omnipotent Good. And if that man had not forsaken that assistance of his free will, he would always have been good; but he forsook it, and he was forsaken. Because such was the nature of the aid, that he could forsake it when he would, and that he could continue in it if he would; but not such that it could be brought about that he would. This first is the grace which was given to the first Adam; but more powerful than this is that in the second Adam. For the first is that whereby it is affected that a man may have righteousness if he will; the second, therefore, can do more than this, since by it it is even effected that he will, and will so much, and love with such ardour, that by the will of the Spirit he overcomes the will of the flesh, that lusteth in opposition to it. Nor was that, indeed, a small grace by which was demonstrated even the power of free will, because man was so assisted that without this assistance he could not continue in good, but could forsake this assistance if he would. But this latter grace is by so much the greater, that it is too little for a man by its means to regain his lost freedom; it is too little, finally, not to be able without it either to apprehend the good or to continue in good if he will, unless he is also  made to will.