7 And let no one be startled at the word “creditor.” We were before under a hard creditor, who was not to be satisfied and paid to the full but by the death of the debtor. The Lord Jesus came, He saw us bound by a heavy debt. No one could pay his debt with the patrimony of his innocence. I could have nothing of my own wherewith to free myself. He gave to me a new kind of acquittance, changing my creditor because I had nothing wherewith to pay my debt. But it was sin, not nature, which had made us debtors, for we had contracted heavy debts by our sins, that we who had been free should be bound, for he is a debtor who received any of his creditor's money. Now sin is of the devil; that wicked one has, as it were, these riches in his possession. For as the riches of Christ are virtues, so crimes are the wealth of the devil. He had reduced the human race to perpetual captivity by the heavy debt of inherited liability, which our debt-laden ancestor had transmitted to his posterity by inheritance. The Lord Jesus came, He offered His death for the death of all, He poured out His Blood for the blood of all.
Source: Letters (New Advent)