The similitude is borrowed from the case of a debtor, to whom a debt of five hundred pence had been forgiven. It is not said that the debt is forgiven because he loved much, but that he loved much because it was forgiven.
A parallel can be observed in the case of a borrower, to whom a debt of five hundred pence has been cancelled. It is not stated that the borrower's affection is great because it has been forgiven, but rather that their affection is great because it has been forgiven.