Exodus 12:12-14

“For I will go through the land of Egypt on that night and strike down every firstborn, both men and animals, and I will execute judgments against all the gods of Egypt. I am ADONAI. The blood will be a sign for you on the houses where you are. When I see the blood, I will pass over you. So there will be no plague among you to destroy you when I strike the land of Egypt. “This day is to be a memorial for you. You are to keep it as a feast to ADONAI. Throughout your generations you are to keep it as an eternal ordinance.