5 If, then, the apostle, who was a chosen vessel separated unto the gospel of Christ, by reason of the pricks of the flesh and the allurements of vice keeps under his body and brings it into subjection, lest when he has preached to others he may himself be a castaway; and yet, for all that, sees another law in his members warring against the law of his mind, and bringing him into captivity to the law of sin; if after nakedness, fasting, hunger, imprisonment, scourging and other torments, he turns back to himself and cries “Oh, wretched man that I am, who shall deliver me from the body of this death?” do you fancy that you ought to lay aside apprehension?
See to it that God say not some day of you: “The virgin of Israel is fallen and there is none to raise her up.” I will say it boldly, though God can do all things He cannot raise up a virgin when once she has fallen. He may indeed relieve one who is defiled from the penalty of her sin, but He will not give her a crown. Let us fear lest in us also the prophecy be fulfilled, “Good virgins shall faint.” Notice that it is good virgins who are spoken of, for there are bad ones as well. “Whosoever looks on a woman,” the Lord says, “to lust after her has committed adultery with her already in his heart.” So that virginity may be lost even by a thought. Such are evil virgins, virgins in the flesh, not in the spirit; foolish virgins, who, having no oil, are shut out by the Bridegroom.
Source: Letters (New Advent)