Shadows are one of God’s favorite tools throughout the Old Testament. These served to help His people understand what He would do later.
For the Law, since it has only a shadow of the good things to come and not the very form of things, can never, by the same sacrifices which they offer continually year by year, make perfect those who draw near. -Hebrews 10:1
The Passover served as the greatest shadow of God’s plan to ultimately redeem His people from sin and death.
For the LORD will pass through to smite the Egyptians; and when He sees the blood on the lintel and on the two doorposts, the LORD will pass over the door and will not allow the destroyer to come in to your houses to smite you. And you shall observe this event as an ordinance for you and your children forever. When you enter the land which the LORD will give you, as He has promised, you shall observe this rite. -Exodus 12:23-25
God told the people they would be saved from the destroyer through their obedience. Blood on the doorposts meant salvation. Lack thereof meant death. Just as the Passover meal was meant to spark memories of what God had done for the Israelites, Christians have been left a memorial feast lest we forget the event the Passover shadowed.
And He said to them, “I have earnestly desired to eat this Passover with you before I suffer; for I say to you, I shall never again eat it until it is fulfilled in the kingdom of God.” And when He had taken a cup and given thanks, He said, “Take this and share it among yourselves; for I say to you, I will not drink of the fruit of the vine from now on until the kingdom of God comes.” And when He had taken some bread and given thanks, He broke it and gave it to them, saying, “This is My body which is given for you; do this in remembrance of Me.” And in the same way He took the cup after they had eaten, saying, “This cup which is poured out for you is the new covenant in My blood.” -Luke 22:15-20
The Passover was observed yearly. It represented the historical moment when God redeemed His people. In a similar but more frequent fashion, the Lord Supper is observed as Christians remember the historical moment when the sacrifice of Jesus first brought salvation to those who obediently place the blood of Christ on our hearts in baptism.
For you are all sons of God through faith in Christ Jesus. For all of you who were baptized into Christ have clothed yourselves with Christ. There is neither Jew nor Greek, there is neither slave nor free man, there is neither male nor female; for you are all one in Christ Jesus. And if you belong to Christ, then you are Abraham’s descendants, heirs according to promise.
-Galatians 3:26-29