As we learned on yesterday’s daf , the Mishna quoted the opinions of Beit Shammai and Beit Hillel who both attempt to limit the spread of ritual impurity at meals. Today’s Gemara quotes a Tosefta that expands on their discussion.
Beit Shammai say: One washes his hands and mixes water with the wine in the cup thereafter, as if you say that one mixes water with the wine in the cup first, his hands will remain ritually impure, as the Sages decreed that unwashed hands have second degree ritual impurity status as if they touched something rendered ritually impure by a creeping animal. Consequently, there is room for concern that the liquid that inevitably drips on the outside of the cup might become ritually impure due to his hands, and those liquids will in turn render the cup ritually impure. Consequently, Beit Shammai said that the hands must be washed first in order to prevent that result.
And Beit Hillel say: One mixes water with the wine in the cup and only washes his hands thereafter, as if you say that one washes his hands first, there is a decree lest the liquid from the outside of the cup that dampened one’s hands will be rendered ritually impure due to the cup which is liable to be impure, and the liquid will in turn render his hands ritually impure.
The halakhot of ritual purity and impurity are among the most complex of Torah laws (Shabbat 31a; see Rashi). However, there are certain fundamental principles that apply universally. Most items that are impure by Torah law, i.e., a dead creeping animal, the carcass of an animal, a leper, and a zav, are primary sources of ritual impurity and render any person or vessel with which they come into contact ritually impure.
A person, vessel, or food which comes into contact with a primary source of ritual impurity becomes a secondary source of ritual impurity and assumes first degree ritual impurity status. The item most sensitive to becoming ritually impure is consecrated meat, which may assume even fourth degree ritual impurity status. Teruma can assume no lower than third degree status and non-sacred items can assume no lower than second decree status. An item that becomes ritually impure but cannot render other items impure is deemed invalid or disqualified, not impure.
To this basic system, the Sages added numerous decrees. One is: Liquids that become ritually impure always assume first degree ritual impurity status. This was a decree due to liquids of a zav (see Shabbat 4b; Bekhorot 38a). Any food item that comes into contact with a ritually impure liquid assumes at least second degree status.