So, then, it is fitting for us to believe both that sinners must repent and that forgiveness is to be given on repentance, yet still as hoping for forgiveness as granted upon faith, not as a debt, for it is one thing to earn, and another presumptuously to claim a right. Faith asks for forgiveness, as it were, by covenant, but presumption is more akin to demand than to request. Pay first that which you owe, that you may be in a position to ask for what you have hoped. Come with the disposition of an honest debtor, that you may not contract a fresh liability, but may pay that which is due of the existing debt with the possessions of your faith.
He who owes a debt to God has more help towards payment than he who is indebted to man. Man requires money for money, and this is not always at the debtor's command. God demands the affection of the heart, which is in our own power. No one who owes a debt to God is poor, except one who has made himself poor. And even if he have nothing to sell, yet has he wherewith to pay. Prayer, fasting, and tears are the resources of an honest debtor, and much more abundant than if one from the price of his estate offered money without faith.
St. Ambrose of Milan, On Repentance, Book II, Chapter 9