The story of Passover starts with a Jewish people enslaved by a cruel Egyptian king. This king, called simply "Pharaoh," has just decided that his slaves are numerous enough to be a threat to his kingdom [source: Chabad].
To cut their numbers, Pharaoh orders the killing of every newborn Jewish male in the land. Moses' mother hides the new baby for as long as she can, and then, to save his life, sends his sister, Miriam, to lay him in a basket on the bank of the Nile, where Pharaoh's daughter regularly bathed [source: Chabad].
The princess finds Moses, takes him home and raises him as a prince. Moses eventually discovers the truth of his ancestry, and when he is grown he leaves the palace [source: Teram]. He becomes a shepherd, and he lives quietly until the day he murders an Egyptian man he finds abusing a Jewish slave. Suddenly a fugitive, despondent, he turns to God.
When Pharaoh refuses, Moses warns him of what will come.
When Pharaoh again refuses, God starts sending the 10 Plagues:
1. The Nile River, Egypt's prime water supply, turns to blood.
2. Frogs rain down from the sky.
3. Dust turns into lice, infesting every Egyptian and animal in Pharaoh's kingdom.
4. Cities are overrun by wild animals.
With each new plague, Pharaoh agrees to free the slaves; and with the ebbing of each new plague, he changes his mind [source: Chabad].
5. Disease kills out all livestock.
6. Agonizing boils cover the skin of every Egyptian.
7. A terrible, destructive hail falls from the sky.
8. Locusts wipe out Egypt's agriculture.
9. A complete, heavy darkness descends on the kingdom.
10. Every firstborn Egyptian male dies.
Before carrying the tenth plague out, God tells Moses to organize an animal sacrifice and smear the creature's blood on the door of every Jewish home.
God then kills each firstborn Egyptian male in Pharaoh's kingdom. They die at midnight on 15 Nissan, 2448 [source: Chabad]. Each Jewish home, marked with blood, is spared – "passed over" by the final plague of death. It is the 10th plague that shatters Pharaoh's resolve, as even his own son dies.
At this, Pharaoh commands the slaves out of his kingdom, and they take little time to pack. Bread for the coming trek has no time to rise. They simply grab the unleavened dough and rush to freedom, and the hot sun bakes the bread flat as they go.
But Pharaoh changes his mind, and by the time the Jews reach the Red Sea, they are trapped between the waters and Pharaoh's army. Moses turns to God, who tells him to strike the sea with his staff.
The waters part, revealing a path of dry land. Just as the last of the Jews makes it to the far bank, the sea comes crashing back together. The soldiers of Egypt drown. The Jews head into the desert, toward Palestine.
Passover commemorates this exodus from slavery to freedom -- and the "unleavened" part of the story plays a central role in the holiday's observance.
In short, all chametz must go.