ALL SINS CAN BE FORGIVEN.
Who does not see how impious and how sacrilegious it is if a person, who has been converted to good things through penance for his past evils, believes that there can be no forgiveness for any sin?[1] What else is being done with these words than that the hand of the all-powerful physician is being pushed away by the vice of despair, from effecting human salvation? For the physician himself says, Those who are healthy do not need a physician, but the sick do.[2] If our physician is an expert, he can cure all maladies. If God is merciful, he can forgive all sins. A goodness that does not conquer every evil is not a perfect goodness, nor is a medicine perfect for which any disease is incurable. It is written in the sacred writings, Against wisdom, evil does not prevail;[3] and the omnipotence of our physician is made known by such words in the psalm: Bless the Lord, O my soul, and all that is within me, bless his holy name. Bless the Lord, O my soul, and do not forget all his benefits—who forgives all your iniquity, who heals all your diseases, who redeems your life from the pit, who crowns you with steadfast love and mercy, who satisfies you with good as long as you live so that your youth is renewed like the eagle’s. What, I ask, do we think cannot be forgiven us when the Lord forgives all our iniquities? Or what do we think cannot be healed in us, when the Lord heals all our diseases? Or how is there anything still lacking to the healed and justified person whose desire is satisfied with good things? Or how is he not believed to gain the benefit of complete forgiveness to whom a crown is given together with love and mercy? Therefore, let no one despairing of the physician remain in his infirmity; let no one, downplaying the mercy of God, waste away in iniquities. The apostle calls out that Christ died for the ungodly.[4]
Letter 7.4