Exodus 12:13-14

The blood shall be for a token or sign to you upon [the doorposts of] the houses where you are, [that] when I see the blood, I will pass over you, and no plague shall be upon you to destroy you when I smite the land of Egypt. [I Cor. 5:7; Heb. 11:28.] And this day shall be to you for a memorial. You shall keep it as a feast to the Lord throughout your generations, keep it as an ordinance forever.