Right at the end of the book of Shemot, there is a textual difficulty so slight that it is easy to miss, yet -- as interpreted by Rashi -- it contains one of the great clues as to the nature of Jewish identity: it is a moving testimony to the unique challenge of being a Jew.

A common feature of traditional Jewish life is washing the hands. On awaking in the morning, one washes one's hands. In the daily prayer book, the first of the morning blessings concerns washing the hands. Before eating bread, one washes the hands, saying the same blessing. The hands of the Kohanim (Priests) are washed by the Levites before they bless the people on a festival.