He next assumes what is not granted by the more rational class of believers, but what perhaps is considered to be true by some who are devoid of intelligence,— viz., that “God, like those who are overcome with pity, being Himself overcome, alleviates the sufferings of the wicked through pity for their wailings, and casts off the good, who do nothing of that kind, which is the height of injustice.” Now, in our judgment, God lightens the suffering of no wicked man who has not betaken himself to a virtuous life, and casts off no one who is already good, nor yet alleviates the suffering of any one who mourns, simply because he utters lamentation, or takes pity upon him, to use the word pity in its more common acceptation. But those who have passed severe condemnation upon themselves because of their sins, and who, as on that account, lament and bewail themselves as lost, so far as their previous conduct is concerned, and who have manifested a satisfactory change, are received by God on account of their repentance, as those who have undergone a transformation from a life of great wickedness.
For virtue, taking up her abode in the souls of these persons, and expelling the wickedness which had previous possession of them, produces an oblivion of the past. And even although virtue do not effect an entrance, yet if a considerable progress take place in the soul, even that is sufficient, in the proportion that it is progressive, to drive out and destroy the flood of wickedness, so that it almost ceases to remain in the soul.
Source: Against Celsus (New Advent)