Passover (Pesach) History
Observance of Passover has taken a number of forms through history. This evolution is partly seen in the Torah text itself. It is discussed as a springtime festival, a barley harvest festival, and a time to bring sacrifices to the Temple in Jerusalem. Different references to Passover in the Torah as well as knowledge of other ancient rituals that took place at the same time of year indicate that there may have been several origins of the Pesach festival. The ancient Israelites took what was originally one or more separate Canaanite spring holidays and imbued them with a heightened significance when they made Pesach a commemoration of the Exodus from Egypt.
We now view commemoration of the liberation of the Hebrews from Egyptian bondage as identical to the celebration of the Feast of Unleavened Bread. In Leviticus (23:5-6), however, there seems to be a distinction between the two festivals. The "Lord's Passover" falls at dusk on the 14th day of the first month, Nisan (referred to in Torah as the month of "Aviv"). The Festival of Unleavened Bread fell on the 15th day of the same month. In Exodus 13:4 and Deut. 16:1, the New Moon is given as the memorial day for the Exodus.
Setting aside, slaughtering, and eating a paschal lamb was introduced as a celebration of the festival. The Hebrews were commanded to take a lamb for each household on the 10th of the first month (Nisan). The unblemished male lamb in its first year was kept until the 14th day and then killed at eve. This ritual was reminiscent of ancient pagan rituals that took place at this time of the year. Nisan was the month when sheep gave birth and sacrifices were made at the full moon on the 15th of the month.
Passover also falls at the time of the beginning of the spring harvest. Leviticus 23:10-16 discusses the omer [a certain measure] of new barley that was brought to the Temple on the second day of the festival. At this time of year, the first sheaf of newly cut barley was offered up as a sacrifice. It has been suggested that the elimination of hametz (leaven), which Jews undertake before Passover, may have originated as a precaution against infecting the new crop. Thus, Hag ha-Matzot (the feast of unleavened bread), which is a name for Passover, may have originally carried this agricultural meaning. Hag ha-Aviv, or Spring Festival, is another name for the festival of Pesach. A number of remnants of the springtime origins of Pesach remain, as in the prayer for dew, and the counting of the Omer that bridges two different spring harvest periods.