Passover is the first and most significant of the Jewish pilgrim festivals (i.e. festivals which since ancient times have been celebrated by Jews in Israel making a pilgrimage to Jerusalem and praying at the site of the Holy Temple).  It celebrates the redemption by God of the Jewish people from slavery in Egypt, and marks the birth of our nation.  Work is not permitted on the first two and last two days. Many Jews refrain from work during the whole festival.