Aside from the monetary obligation to pay back a loan, there is a mitzva to do so, as well. Furthermore, according to the Mishna, if a person borrows money and a promissory note is written, then his property becomes obligated to the debt, and the lender can collect the debt from that property even if it has been sold to a third party. If, however, the loan was made in front of witnesses, but no note was written, then repayment can only be made from property that the borrower is still holding.
This clear halakha notwithstanding, we find a disagreement about how property becomes obligated to the repayment of that debt.
According to Ulla, all loans – whether they are committed to writing or done in front of witnesses – obligate the borrower’s property, which theoretically can be collected as payment even if it has been sold. Ulla argues that the basis for this rule is biblical, and that the Sages limited it only to loans that are committed to writing because only then can we be certain that the individual who purchased the land from the borrower would know that there was a lien on it. When the loan only had witnesses, we are concerned lest the buyer will unfairly lose his purchase.
According to Rabba, biblical law does not recognize the automatic creation of a lien on property in any case of borrowing. The Sages enacted a rule obligating the borrower’s property to pay the loan in order to offer a guarantee to the lender so that loans would be readily available. This rule was limited to cases where we could be certain that the purchaser would hear about the lien, that is, only cases where a formal note was written.
The Ramah explains that according to Ulla the biblical law obligated all of the borrower’s property to the repayment of the debt – both real estate and moveable property. The Sages limited the lien only to real estate out of concern that it would be impossible for people to keep track of liens on moveable property, and every purchase might be collected for unpaid debts.