Exodus 12 opens with God giving Moses and Aaron detailed instructions for what would become the first passover. God declared that this month would mark the beginning of the Hebrew calendar year. Each household was instructed to select an unblemished male lamb on the tenth day of the month and keep it until the fourteenth day, at which point the entire assembly of Israel was to slaughter their lambs at twilight.

The Israelites were then told to apply the lamb's blood to the doorposts and lintel of their homes. That night, they were to roast the lamb and eat it with unleavened bread and bitter herbs, fully dressed and ready to travel — sandals on their feet, staff in hand — eating in haste. God warned that anything left over by morning was to be burned. This meal was to be eaten with urgency, because the Lord would pass through Egypt that night and strike down every firstborn, both human and animal, executing judgment on all the gods of Egypt. The blood on the doorposts would serve as a sign, and God would "pass over" those houses, sparing them from the plague of death.

God then commanded that this day be commemorated as a lasting ordinance throughout all generations. The feast of unleavened bread was instituted alongside the passover, lasting seven days, during which no leaven was to be found in any Israelite home. The first and seventh days were to be held as sacred assemblies, and all work was to cease on those days. Moses relayed all of these instructions to the elders of Israel, and the people bowed in worship and carried out everything God had commanded.

At midnight, the plague struck Egypt. Every firstborn in the land died — from the firstborn of Pharaoh on his throne to the firstborn of the prisoner in the dungeon, along with all the firstborn of the livestock. A great cry went up throughout Egypt, for there was not a house without someone dead.

Pharaoh summoned Moses and Aaron in the night and urgently commanded them to leave, telling them to take their flocks and herds and go, blessing him as they left. The Egyptians, gripped with fear, urged the Israelites to leave quickly, pressing them to go before any more death came upon them.

The Israelites left in haste, carrying their unleavened dough before it could rise. They also plundered the Egyptians by requesting silver, gold, and clothing, and the Egyptians gave them what they asked for. The Israelites journeyed from Rameses to Succoth — a group numbering about six hundred thousand men on foot, not counting women and children, along with a great mixed multitude and their livestock.

Exodus 12 closes with a reaffirmation of the passover regulations. It was stressed that no foreigner or uncircumcised person was permitted to eat the passover meal. However, any slave who had been circumcised could participate, as could a foreigner who had been circumcised and joined the community. The meal was to be eaten inside the house, and none of the lamb's bones were to be broken. The chapter concludes by noting that, on that very day, God brought the Israelites out of Egypt division by division, fulfilling His promise to His people.