Exodus 12:13-14

The blood shall be a sign for you on [the doorposts of] the houses where you live; when I see the blood I shall pass over you, and no affliction shall happen to you to destroy you when I strike the land of Egypt. [1 Cor 5:7; Heb 11:28] ‘Now this day will be a memorial to you, and you shall keep it as a feast to the LORD; throughout your generations you are to celebrate it as an ordinance forever.