Exodus 12:3, 6-7, 12-13

Tell all the congregation of Israel, ‘On the tenth [day] of this month they are to take a lamb or young goat for themselves, according to [the size of] the household of which he is the father, a lamb or young goat for each household.

You shall keep it until the fourteenth day of the same month, then the whole assembly of the congregation of Israel is to slaughter it at twilight. Moreover, they shall take some of the blood and put it on the two doorposts and on the lintel [above the door] of the houses in which they eat it. [Matt 26:28; John 1:29; Heb 9:14]

For I [the LORD] will pass through the land of Egypt on this night, and will strike down all the firstborn in the land of Egypt, both man and animal; against all the gods of Egypt I will execute judgments [exhibiting their worthlessness]. I am the LORD. 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]