Pesach חג הפסח
The festival of the Exodus: seven days without leaven, the seder, and telling children the story of the going out.
Pesach is instituted before the Exodus itself: a lamb is taken on the tenth of Nisan, offered on the fourteenth, and eaten on the night of the fifteenth with matzah and bitter herbs, the doorposts marked with blood. That night the people leave Egypt without waiting for the dough to rise — hence matzah, at once the bread of poverty and the bread of haste.
The festival's central commandment is not eating but telling: «you shall tell your child on that day». The seder is built as a lesson for children — four questions, four sons, four cups, matzah and maror on the table so that they ask. The Haggadah requires each person to see himself as having left Egypt.
For seven days leaven may not even be owned, hence the cleaning, the search by candlelight and the sale of chametz.