If you make a vow to the Lord your God, do not be slow to pay it, for the Lord your God will certainly demand it of you and you will be guilty of sin.
This passage seems to relate back to the idea of cancelling all loans and debts after seven years, because the amount of money I imagine people were borrowing back then could easily be repaid in seven years time as long as they made the effort to do so. Also the theme of instilling the fear of God in someone is frequent in this aspect as well, and was probably the only means of persuasion other than death.