Nicene and Post-Nicene Fathers, Ser. II, Vol. XI:
The Works of John Cassian.: Chapter V. Of the method of penitence and the proof of pardon.

Chapter V.

Of the method of penitence and the proof of pardon.

Wherefore in order to satisfy as briefly and shortly as possible, your desire and question, the full and perfect description of penitence is, never again to yield to those sins for which we do penance, or for which our conscience is pricked. But the proof of satisfaction and pardon is for us to have expelled the love of them from our hearts. For each one may be sure that he is not yet free from his former sins as long as any image of those sins which he has committed or of others like them dances before his eyes, and I will not say a delight in—but the recollection of—them haunts his inmost soul while he is devoting himself to satisfaction for them and to tears. And so one who is on the watch to make satisfaction may then feel sure that he is free from his sins and that he has obtained pardon for past faults, when he never feels that his heart is stirred by the allurements and imaginations of these same sins. Wherefore the truest test of penitence and witness of pardon is found in our own conscience, which even before the day of judgment and of knowledge, while we are still in the flesh, discloses our acquittal from guilt, and reveals the end of satisfaction and the grace of forgiveness. And that what has been said may be more significantly expressed, then only should we believe that the stains of past sins are forgiven us, when the desires for present delights as well as the passions have been expelled from our heart.