Jewish custom now normally associated with meals started with Temple purity.
Reprinted from The Jewish Religion: A Companion, published by Oxford University Press.
In Temple times there were elaborate rules in connection with ritual impurity. If a person had been rendered impure through having come into contact, say, with a dead rodent, he contaminated sacred food such as the tithe given to the priests, which must then not be eaten. The way in which contamination of this kind could be removed was through immersion in a ritual bath.
But the sages imposed in certain circumstances the minor form of contamination known as "hand contamination" in which only the hands, not the whole body, was contaminated and for this to be removed total immersion was not required, only the ritual washing of the hands. Since there was a good deal of priests' tithe in ancient Palestine which could easily come into contact with the hands, the sages eventually ordained that the hands of every Jew, not only the hands of a priest, must be washed ritually before meals.
Not a Matter of Hygiene
It has to be appreciated that this ritual washing of the hands has nothing to do with physical cleanliness. On hygienic grounds, the hands are obviously to be clean of dirt before food is eaten. Even when the hands are physically clean they are still required to be ritually washed.
Although the original reason for washing the hands no longer applies, since there is no sacred food to be eaten, the ritual was continued on the grounds that the ideal of holiness demands a special, ritualistic washing of the hands. The act of washing the hands in this sense is seen as the introduction of the holiness ideal into the mundane life of the Jew. This ritual washing is only required before a meal at which bread is eaten.
Procedure and Practice
The procedure is to pour water out from a cup or glass first twice over the right hand and then twice over the left hand--care being taken that the unwashed hands do not touch the water used for the washing. The hands are then dried with a towel before partaking of the meal. A benediction is recited over the washing of the hands: "Blessed art Thou, O Lord our God, King of the universe, who has sanctified us with Thy commandments and has commanded us concerning the washing of the hands."
The reference to the command has to be understood in the context that rabbinic ordinances are also commanded by God. Observant Jews are very strict in this matter of washing the hands before meals.
The Talmud also refers to washing the hands after meals but here the reason given is that people used to eat with their hands and a certain salt added to food in those days might cause injury to the eyes if it came into contact with them. The French authorities in the Middle Ages argued that this hygienic reason no longer obtains, since this kind of salt is no longer used.