The Mishna (37a) teaches that just as a person cannot walk more than 2,000 cubits outside of the city limits (called tehum) on Shabbat and Yom Tov, his or her possessions are limited, as well. In Massekhet Eiruvin we learned that by means of an eiruv tehumim – by placing a meal at the edge of the city limits – a person can establish his Shabbat in that place, thus shifting the area that he is allowed to travel to 2,000 cubits around that space. Thus, if a person were to lend something to his friend on Yom Tov, it can only be taken as far as its owner is allowed to walk, even if the borrower has made an eiruv that permits him to travel further than that. One example presented by the Mishna is a woman who lends water and salt to her friend to bake bread on Yom Tov. The final product will be limited to the extent that it can only be taken to places that both the borrower and the lender themselves could go.
The Gemara on our daf describes a discussion among the amora’im about this rule. Three Israeli amora’im were discussing this matter (either Rabbi Yohanan, Rabbi Hanina bar Pappi and Rabbi Zeira or else Rabbi Abbahu, Rabbi Shimon ben Pazi and Rabbi Yitzhak Nappaha) and queried why this should be true; shouldn’t the water and salt be considered batel – negligible – in the context of the final baked product!?
Rabbi Abba said to them: If one’s single kav of wheat became mingled with ten kav of another’s wheat, shall the latter eat all eleven kav and rejoice? One does not allow his property to become nullified into someone else’s property. The same applies to water and salt in dough. The Sages laughed at him. He said to them: Did I take your cloaks from you that you are putting me to shame? They again laughed at him.
This interaction is particularly interesting because the Gemara begins the story with a description of the prayer recited by Rabbi Abba upon embarking on his trip from Babylonia to Israel, in which he expressed his hope that his thoughts and ideas would be accepted by the scholars of Israel. The Hatam Sofer explains that the Sages who lived in Israel recognized their own knowledge of Torah, and often looked down on the Torah that was studied and taught in Babylon, which brought a visiting scholar to be concerned lest his ideas would not be taken seriously.