2 The Holy Spirit speaks in the sacred Scriptures, and says, “By almsgiving and faith sins are purged.” Not assuredly those sins which had been previously contracted, for those are purged by the blood and sanctification of Christ. Moreover, He says again, “As water extinguishes fire, so almsgiving quenches sin.” Here also it is shown and proved, that as in the layer of saving water the fire of Gehenna is extinguished, so by almsgiving and works of righteousness the flame of sins is subdued.
And because in baptism remission of sins is granted once for all, constant and ceaseless labour, following the likeness of baptism, once again bestows the mercy of God. The Lord teaches this also in the Gospel. For when the disciples were pointed out, as eating and not first washing their hands, He replied and said, “He that made that which is within, made also that which is without. But give alms, and behold all things are clean unto you;” teaching hereby and showing, that not the hands are to be washed, but the heart, and that the foulness from inside is to be done away rather than that from outside; but that he who shall have cleansed what is within has cleansed also that which is without; and that if the mind is cleansed, a man has begun to be clean also in skin and body.
Further, admonishing, and showing whence we may be clean and purged, He added that alms must be given. He who is pitiful teaches and warns us that pity must be shown; and because He seeks to save those whom at a great cost He has redeemed, He teaches that those who, after the grace of baptism, have become foul, may once more be cleansed.
Source: The Treatises of Cyprian (New Advent)