35 But you, beloved brethren, whose fear is ready towards God, and whose mind, although it is placed in the midst of lapse, is mindful of its misery, do you in repentance and grief look into your sins; acknowledge the very grave sin of your conscience; open the eyes of your heart to the understanding of your sin, neither despairing of the Lord's mercy nor yet at once claiming His pardon. God, in proportion as with the affection of a Father He is always indulgent and good, in the same proportion is to be dreaded with the majesty of a judge.
Even as we have sinned greatly, so let us greatly lament. To a deep wound let there not be wanting a long and careful treatment; let not the repentance be less than the sin. Think you that the Lord can be quickly appeased, whom with faithless words you have denied, to whom you have rather preferred your worldly estate, whose temple you have violated with a sacrilegious contact? Think you that He will easily have mercy upon you whom you have declared not to be your God? You must pray more eagerly and entreat; you must spend the day in grief; wear out nights in watchings and weepings; occupy all your time in wailful lamentations; lying stretched on the ground, you must cling close to the ashes, be surrounded with sackcloth and filth; after losing the raiment of Christ, you must be willing now to have no clothing; after the devil's meat, you must prefer fasting; be earnest in righteous works, whereby sins may be purged; frequently apply yourself to almsgiving, whereby souls are freed from death. What the adversary took from you, let Christ receive; nor ought your estate now either to be held or loved, by which you have been both deceived and conquered. Wealth must be avoided as an enemy; must be fled from as a robber; must be dreaded by its possessors as a sword and as poison. To this end only so much as remains should be of service, that by it the crime and the fault may be redeemed. Let good works be done without delay, and largely; let all your estate be laid out for the healing of your wound; let us lend of our wealth and our means to the Lord, who shall judge concerning us. Thus faith flourished in the time of the apostles; thus the first people of believers kept Christ's commands: they were prompt, they were liberal, they gave their all to be distributed by the apostles; and yet they were not redeeming sins of such a character as these.
Source: The Treatises of Cyprian (New Advent)