Sotah, Chapter Four, Mishnah Four
In the previous several mishnayoth, we learned of several categories of women who do not drink the water. Our mishnah adds certain women that do, even though it might be supposed that they should not.
1) The wife of a priest drinks and [if she is found to be innocent] is permitted to her husband.
2) The wife of a eunuch drinks.
3) Through [seclusion with] all persons forbidden to her in marriage wives are subjected to warning with the exception of a minor and one not a human.
Section one: The sexual prohibitions for a priest are more stringent than they are for a non-priest. For instance, if the wife of a priest is raped, the priest may not stay married to her. Therefore, the mishnah comes to teach that if she drinks the water, and the water does not cause the negative effects, she may remain married to her husband.
Section two: Even though a eunuch cannot have chidren, he may remain married to his wife. If she becomes a sotah, she drinks the water as does a regular wife.
Section three: Chapter one began by describing the process whereby a husband warns his wife not to be secluded with a certain man. If she is secluded with that man in front of witnesses she becomes a sotah and must drink the water in order to clear her name. Our mishnah teaches that the husband may warn her not to be secluded even with men prohibited to her, such as her father or her son. This is true even though a woman may normally be secluded with either of them. The only two categories of women with regard to whom he cannot warn her are children and animals. These two categories are excluded by a midrash on the word ish (man) in Numbers 5:13. Ish excludes animals and minors. If the husband warns her not to be secluded with them and she is secluded with them she doesnt drink the water and she is not prohibited to her husband.