God Provided
God provided protection for His people: Death was coming, and blood was the only thing that could save you. Kill a spotless (perfect and without blame) lamb and mark your door with its blood. Death would literally PASS OVER your home, and those inside would be spared. All you had to do was believe enough to do it.
Read all about it here.
The Israelites had just witnessed some pretty serious stuff. The Nile had turned to blood. Bugs and frogs everywhere. But this was the only plague that came with an "opt-out" moment. Serious stuff: Wanna protect the first-born inside? Paint the doorway and stay inside. Protection for the price of a lamb.
God provided a Lamb for us.
We, too, are facing death. Eternal death and separation from God. Blood is still the only thing that will save anyone. But the Lamb for us was Jesus, and His blood on the cross was our doorway protection.
That night - the original Passover - the LORD Himself went through the land to check the doors. (Exodus 12: 23) He didn't leave a job this important to someone else. He alone checked to see who had believed.
It's all about the cross.