Today’s religious holiday stems from the bible to include murder and a meal for circumcised men. Yeah, it’s weird.
God was angry with the Egyptian Pharaoh for not releasing Israelite slaves and afflicted punishment in the form of ten plagues. The Passover was plague number ten.
From Sex in the Name of God, Chapter 2: The Penis Pact
Great detail was given about how to select, prepare, and cook a lamb.
Exodus 12 43 The LORD said to Moses and Aaron, “This is the ordinance of the Passover. No foreigner shall eat of it, 44 but every man’s servant who is bought for money, when you have circumcised him, then shall he eat of it. 45 A foreigner and a hired servant shall not eat of it. 46 It must be eaten in one house. You shall not carry any of the meat outside of the house. Do not break any of its bones. 47 All the congregation of Israel shall keep it. 48 When a stranger lives as a foreigner with you, and would like to keep the Passover to the LORD, let all his males be circumcised, and then let him come near and keep it. He shall be as one who is born in the land; but no uncircumcised person shall eat of it.”