The Torah and the the Bible both tell the story in the book of Exodus of how the Hebrew people (known as the Israelites) struggled as slaves in Egypt, yet remained faithful to God even under pressure from the Egyptians to turn their backs on their faith. God sent 10 plagues on Egypt to get the attention of Pharaoh (the Egyptian leader) and try to convince him to give the Israelites their freedom.
Passover derives its name from the last plague, in which an angel of death killed the firstborn human son and the firstborn animal from every Egyptian family, but passed over the Hebrew families, who had followed God's instructions to place a symbol of their faith (blood from sacrificial lambs) on the doorposts of their homes. Here's more about the Passover miracle:
Instructions from God
The book of Exodus records in chapter 11, verse 1 God telling Moses, an Israelite leader: "I will bring one more plague on Pharaoh and on Egypt. After that, he will let you go from here...". Then God announced that the firstborn male child and animal of every Egyptian family would die during a night God chose to show the Egyptian people his judgment for their sin and the Hebrew people his blessing for their faithfulness.
God gave the Israelites detailed instructions about how they should prepare for that night, when he would send an angel of death to Egyptian homes. In Exodus chapter 12, God explains how he wants the Israelites to sacrifice lambs and use blood from the slaughtered animals to mark their homes as the dwellings of faithful people. He tells Hebrew leaders Moses and Aaron: "Then they are to take some of the blood and put it on the sides and tops of the doorframes of the houses where they eat the lambs," says verse 7. Since the blood was considered to be a precious sacrifice, it wasn't placed on the bottoms of the doorframes, where it could be stepped on.
The Passover story continues with God telling Moses and Aaron what they should tell the Israelites about what will happen in the middle of the night: "When the Lord goes through the land to strike down the Egyptians, he will see the blood on the top and sides of the doorframe and will pass over that doorway, and he will not permit the destroyer to enter your houses and strike you down" (Exodus 12:23).
A few verses later, in Exodus 12:29, the Torah and the Bible say that, "At midnight the Lord struck down all the firstborn in Egypt, from the firstborn of Pharaoh, who sat on the throne, to the firstborn of the prisoner, who was in the dungeon, and the firstborn of all the livestock as well."
The result was what God had predicted -- Pharaoh finally let the Hebrew go free: "During the night Pharaoh summoned Moses and Aaron and said, 'Up! Leave my people, you and the Israelites! Go and worship the Lord as you have requested" (Exodus 12:31).
God intervened miraculously to help the Israelites to show how sacred freedom is to him, writes Calvin Miller in his book Miracles and Wonders: How God Changes His Natural Laws to Benefit You: "Human significance lies behind the whole Passover miracle, but the freedom of God is also at stake. It wasn't Moses who said, 'Let my people go!' It was God. God acted in the interest of human freedom, for he himself is free. He cannot be imprisoned in the natural world."
Today, the Passover miracle symbolizes the spiritual freedom that God gives people every day to make a fresh start in their relationships with him, writes Harvey E. Goldberg in his book The Life of Judaism: "Passover, more than any other holiday, represents the possibility of another chance, of wiping the slate clean, of a fresh start."