Yoma, Chapter Eight, Mishnah One
The eighth chapter of Yoma is the chapter that is still relevant in halakhah today. It discusses how we understand the biblical command to afflict oneself (see Leviticus 16:29-31; 23:26-32) as well as the rules and concepts regarding atonement.
Our mishnah begins this discussion by teaching the five/six prohibitions that all fit under the category of afflictions.
1) [On] Yom HaKippurim it is forbidden to eat, to drink, to wash, to anoint oneself, to put on sandals, or to have intercourse.
2) A king or bride may wash their face, and a woman after childbirth may put on sandals, the words of Rabbi Eliezer.
a) But the sages forbid it.
Section one: According to the Babylonian Talmud there are five prohibitions (eating and drinking is considered only one prohibition), which are derived from the fact that the root for afflict oneself appears five times in the Torah in connection with Yom Kippur. However, the Yerushalmi understands these as six prohibitions and does not connect them directly with the verses. These are just how the rabbis understood the meaning of afflict oneself. Putting on sandals refers to wearing leather shoes, whether they are sandals or closed shoes.
Section two: In this section we learn that there are some exceptions to the general prohibitions. A king or a bride may wash their face. The king must look good in order to garner the respect of his people so we want him to look clean. The rabbis want the bride to look beautiful for her husband, in order to help solidify the marriage. They considered the first few days of marriage to be critical and to a certain extent were willing to relax some other prohibitions. In our case, they allowed her to wash her face. The woman after childbirth will be bothered by walking on the cold floor and therefore she is allowed to wear sandals. Although the sages dispute these exceptions, the halakhah is like Rabbi Eliezer.
We should note that the mishnah does not allow any exceptions for eating/drinking. Some commentators derive from here that the prohibitions of eating/drinking are weightier than the others and hence cannot be waived under any circumstance (with the exception of issues of health).