How Long is Passover?
The Book of Exodus says the following: “This day shall be to you one of remembrance; you shall celebrate it as a festival throughout the generations…seven days you shall eat unleavened bread…on the first day you shall hold a sacred convocation, and on the seventh day a sacred convocation; no work at all should be done on them…”
As you can see, the Torah indicates that Pesach is to last seven days and the first and last days of the holiday are to be special. For Reform Jews, that means holding services on the first and seventh days. For others, this means holding services on days 1 and 2 plus days 7 and 8.
Conservative and Orthodox Jews “double” the first and last days because, long ago when the Jewish calendar was set month by month, uncertainty about the exact date of festivals outside Israel arose. To be sure they “got it right,” early Jews therefore celebrated two days of the festival. That way they hoped not to miss the proper day.
Now that the calendar is fixed, Reform Jews have returned to the original biblical commandment. We celebrate Passover for seven days. Others have maintained the double days as a reminder of the way it used to be done.