The sixth perek (=chapter) of Masekhet Arakhin, which began on yesterday’s daf (=page) deals with the evaluation of real estate for the purpose of redeeming it from the Temple. As an aside it begins with a discussion of the method used to evaluate the worth of an estate that is necessary when the person who died left debts to different people. This is necessary specifically in a case where the heirs are underage minors who are unable to take responsibility for the financial affairs of the estate on their own.
On today’s daf the Gemara relates the following story:
Rav Nahman said: At first I would not seize upon the property of orphans to guarantee the payment of debts, but when I heard the statement of our colleague, Rav Huna in the name of Rav: “As for orphans who enjoy what does not belong to them, let them follow him who left them!” from that time on I seize their property.
The Gemara asks why Rav Nahman originally refrained from collecting from the orphans, and Rav Papa explains that the paying of a debt is a commandment and orphans who are underage are not obliged to fulfill the commandments.
The idea that “paying a debt is a commandment” is not a mitzvah that is found clearly stated in the Torah, although the Radbaz in a responsum argues that its source is Sefer Vayikra 5:23 “…he shall restore that which he took by robbery, or the thing which he hath gotten by oppression, or the deposit which was deposited with him, or the lost thing which he found.” Rav Papa’s argument is based on his opinion that the Torah does not place an automatic lien on the property of an individual in order to guarantee repayment of a loan, rather the method it uses to coerce the borrower to repay his loan is by making it a mitzvah. For this reason, children under the age of Bar Mitzvah would not be obligated to repay the loan until they become old enough to do so.
Rav Huna’s argument is that some kind of lien – either Biblical or imposed by the Sages – does exist, so there is no reason to refrain from collecting from the estate, unless there is reason to suspect that the father had paid off the loan while still alive.