God instructs the Israelites to eat a passover lamb and spread its blood on their doorposts as a sign of redemption, a sign to the people. We know that God is going to smite the Egyptian firstborn (except for Pharaoh himself) about midnight of the night Moses left his presence for the final time (Genesis 10:29-11:8). Now, God is instructing Israel to take a lamb and keep it until the fourteenth day of the month and them slaughter it at twilight. 14 days is greater than 1. It seems that God’s final plague will come 13 days before the Israelites paint their doorposts as a sign to avoid the plague. But, look at the wording in verse 1, “Now the Lord said to Moses and Aaron.” There are no timing references. At some point the Lord had given Moses and Aaron these instructions. We are receiving necessary background information for something that is happening on this night. Israel has been prepared. When an apparent contradiction is Scripture is presented to us, it is important for us to read the text as it is, not as it is twisted by many who wish to force contradictions.
God provides some basic instructions. The people are not to portion more than they can eat. The sacrifice is also a meal for them. It is to be roasted. The most important detail, though, is the instructions concerning the blood of the lamb. It is to be spread on the doorposts and lintel of their houses. The door is the entryway to the house. Blood represents life. In fact, this sacrifice is the prototype of the sacrificial lamb and a direct foreshadowing of the Christ, the lamb of God. The sacrificing of the lamb represents Israel’s redemption from slavery in Egypt and ultimate redemption from sin. God passes over those redeemed by the blood of the lamb. This is why Israel celebrates Passover every year on the first Hebrew month. It is why Christians observe the Eucharist (Communion or The Lord’s Supper).
This blood is a sign to the people on their own houses. By celebrating Passover or observing the Eucharist now, we also remember what we were delivered from. When God sees the blood, He personally passes over the people, and no plague will befall them to destroy them when God strikes the land of Egypt. When the sacrificial blood of Christ is seen on us, God sees it and passes over us, and no condemnation will befall us to destroy us when God judges the hearts of people. God shows that it is He Himself who passes through Egypt and takes the firstborn. It is God alone who spares His people from His just wrath on the land.