During Temple times, those who were fulfilling the mitzva of aliya la-regel – pilgrimage to the Temple on the holidays of Pesah, Shavu’ot and Sukkot – needed to immerse themselves in a mikvah in order to ensure a high level of ritual purity. What happened when Yom Tov fell out on Sunday? Could the immersion be done on Shabbat in preparation for the holiday?
The Mishna (17b) teaches that Beit Shammai insisted that, in such a case, immersions had to be done before Shabbat. Beit Hillel allowed people to go to the mikvah on Shabbat, but rule that any utensils that were needed had to be immersed before Shabbat.
Many explanations are offered in the Gemara as to why Beit Hillel differentiated between a person and his utensils. According to Rava, immersing a utensil appears to be tikkun keli – fixing the utensil – which is forbidden on Shabbat, while a person appears to be simply cooling himself off. The Gemara argues that even on Yom Kippur, when bathing is ordinarily forbidden, such an immersion would be permitted since it is permitted on Shabbat, as well. The Re’ah explains that this logic is based on the fact that bathing on Yom Kippur is forbidden only when it is solely for pleasure, which is not the case when someone immerses in the mikvah for reasons of ritual purity.
We learn in a mishna: One who is concerned about pain in his teeth may not sip vinegar through them on Shabbat in order to alleviate his toothache; however, he may dip his food in vinegar in his usual manner during the meal and eat it, and if he is healed by the vinegar, he is healed.
In this parallel case brought by the Gemara, there is an activity that would be forbidden, but when done under circumstances where appearances indicate that it is being done for another reason, it is permitted. This Mishna in Shabbat (111a) teaches that someone with a toothache cannot sip vinegar on Shabbat because of the Rabbinic ruling that medicine cannot be taken on Shabbat except in cases of danger to life. If, however, he is eating bread, he can dip his bread into the vinegar and eat it, even though it will have the same effect, since this appears to simply be an act of dining.
Vinegar was a popular remedy for toothaches in Talmudic times. When a person has a cavity – particularly when the nerve becomes exposed – vinegar is a painful drink, indeed (see Mishlei 10:26). However, when the gums are irritated, or when fluid builds up in the gums, vinegar can offer relief by lowering the osmotic pressure.