God is painting a picture of what is to come.

3 Announce to the whole community of Israel that on the tenth day of this month each family must choose a lamb or a young goat for a sacrifice, one animal for each household. Exodus 12:3

6 “Take special care of this chosen animal until the evening of the fourteenth day of this first month. Then the whole assembly of the community of Israel must slaughter their lamb or young goat at twilight. 7 They are to take some of the blood and smear it on the sides and top of the doorframes of the houses where they eat the animal Exodus 12:6-7 

12 On that night I will pass through the land of Egypt and strike down every firstborn son and firstborn male animal in the land of Egypt. I will execute judgment against all the gods of Egypt, for I am the Lord! Exodus 12:12

13 But the blood on your doorposts will serve as a sign, marking the houses where you are staying. When I see the blood, I will pass over you. This plague of death will not touch you when I strike the land of Egypt. Exodus 12:13

4 cups of the passover meal 

4 fold promise during the exodus in Egypt