On yesterday’s daf we learned some of the rules of ma’aser sheni – “the second tithe.” Ma’aser sheni is the additional tithe that is separated by the farmer after he has given teruma to the kohen and the first tithe to the levi. During the first, second, fourth and fifth years of the shemitta cycle an additional tenth of the produce is set aside by the farmer, who takes it to Jerusalem to eat (during years three and six the tithe is given to the poor). Recognizing that it might be difficult to bring a large amount of crops to Jerusalem, the Torah itself allows the farmer to redeem his crops and take the money to Jerusalem, where he could buy any food products there (see 14:26). Aside from the value of the ma’aser sheni itself, the owner is required by the Torah to add one-fifth as a penalty (or, perhaps, as a “service charge”) for redeeming the fruit rather than bringing it to Jerusalem.
Our Gemara asks whether this additional one-fifth is an absolute requirement or if the ma’aser sheni can be eaten if it is paid for even if this additional sum is not added to the redemption fee.
To answer this question, the Gemara quotes a baraita where Rabbi Eliezer rules that ma’aser sheni without the additional fifth can be eaten, while Rabbi Yehoshua rules that it cannot be eaten. Rebbi (Rabbi Yehuda HaNasi) accepts Rabbi Eliezer’s position on Shabbat (to honor with this food, the Sages allowed it to be eaten) and Rabbi Yehoshua’s position during the week.
The first approach that the Gemara takes is to suggest that Rabbi Eliezer believes that the additional one-fifth is not an absolute requirement, while Rabbi Yehoshua believes that it is. Rav Pappa rejects this conclusion, arguing that neither believe it to be an absolute requirement, and the argument is whether we fear that the individual will not be responsible enough to pay the additional charge.
The Maharatz Hayyut asks why the Gemara did not consider the possibility that all agree that the extra payment is an absolute requirement, but it is one that the Sages pushed aside in the interest of oneg – honoring Shabbat. He answers based on the Rashba that the Sages’ ability to push aside biblical law is limited, and were it forbidden to eat ma’aser sheni that was not redeemed properly, they do not have the ability to push aside that law.