According to the Mishna, a shomer hinam (unpaid bailee) – someone who agrees to watch an object without receiving any payment – does not have to pay the owner for the object if it is lost or stolen. In such cases, he can simply take an oath that he watched the object in a reasonable fashion and he is free of any further obligation. The Mishna does consider the possibility that a shomer hinam might insist on paying rather than taking an oath, in which case, he would receive payment in the event that the thief is found.
The Gemara on our daf introduces Rav Huna who rules that with a shomer hinam who chooses to pay rather than take an oath, we will, nevertheless, require him to swear that he does not have the object in his possession, since we fear lest einav natan bo (literally “he put his eyes on it,” i.e. he may have decided that he wants the object). The Rashba and Ran point out that Rav Huna’s ruling is unexpected because by agreeing to pay, the shomer hinam appears to be a scrupulously honest person. Our concern is not about stealing – which the shomer hinam recognizes is forbidden – but about lo tahmod – “Do not covet” – which people do not realize is forbidden if the object is paid for.
Although the Rambam understands that this oath is a Rabbinic enactment, other rishonim suggest that it is a biblical obligation (see Shemot 22:7). The ruling of the Shulhan Arukh (Hoshen Mishpat 295:1) limits Rav Huna’s ruling only to unique objects, where we have reason to suspect that the shomer hinam may desire it. If, however, the object is one that is readily available for purchase, there is no need to make the shomer hinam swear that he has not taken it for himself.