The Impurity of the Hands
טומאת הידיים
Netilat yadayim (ritual washing of the hands) is one of the seven mitzvot instituted by the Sages. To understand the root of their enactment, we must first explain that according to the Torah, the entire body is considered a single unit with regard to impurity and purity: it is either entirely pure or entirely impure. That is, if one of the body’s limbs touches a source of impurity, the entire body becomes impure. For example, if one touches a corpse with his foot, not only his foot but his entire body becomes impure. Likewise, purification must encompass the entire body; therefore, when a person immerses in a mikveh to purify himself, he must immerse his entire body at once in the water.
In addition to this law, the Sages determined that the hands have a special, separate status. Since they are involved in all practical and material matters, they get dirtier than the rest of the body, and they are also liable to touch impure things unintentionally. The Sages therefore determined that ordinary hands are considered impure, and the way to purify them is by washing them with water (see Rashi, Shabbat 14a).
This enactment went through several stages. In the First Temple period, King Shlomo instituted impurity of the hands with regard to sacrifices: anyone who comes to touch a sacrifice with his hands must first purify them, and if he touched it without purifying his hands, he made the sacrificial meat impure and disqualified it from being eaten. In the Second Temple period, Beit Shammai and Beit Hillel instituted that the hands are impure with regard to teruma as well: anyone who touches teruma without washing disqualifies it from being eaten, and it must be burned so that people will not stumble by eating it (Shabbat 14). Afterward, the Sages expanded the mitzva and determined that it is forbidden to eat bread without washing the hands (Ḥullin 106a).
Two reasons are given for the mitzva of washing before eating bread. The first is on account of serakh teruma (a practice modeled on teruma). That is, so that the kohanim would become accustomed to washing their hands before eating teruma, the Sages instituted that all Jews wash their hands before a meal. In this way, the custom of washing would take root among all of Israel, and the kohanim would be reinforced in washing their hands before eating teruma. And although today the Temple is destroyed and, since there is no way to purify oneself from corpse impurity, the kohanim have not eaten teruma for many generations, the enactment of washing has not been annulled, for the Temple will be rebuilt speedily, and we must be prepared and accustomed to the practices of purity. The second reason is that the hands are busy and in the process touch dirty places, and it is not proper to eat with soiled hands. Thus, in order to preserve the purity and holiness of eating, the Sages instituted netilat yadayim before a meal. They based their words on the verse (Vayikra 11:44): “Sanctify yourselves and be holy, for I am holy” – “‘Sanctify yourselves’ – this refers to the first waters” (Berakhot 53b). Even one whose hands are clean, for instance because he just washed them with soap and water, must wash his hands before eating bread in order to purify and sanctify them for the meal (see SA OḤ 158:1; MB ad loc. 1).