9 plagues had pummelled Egypt but their leader would not submit to the authority and power of the One True God. God would not bring a final plague/judgment upon the land. Pharoah had killed the sons of Israel and now God would return judgment upon he and his people in a similar fashion.
The Lord would come through Egypt and take the life of every firstborn son and male animal. This would be a devastating judgment. Moses told Israel it was coming. He also told them of the hope of avoiding this plague themselves. If their own firstborn sons were to survive then they must follow these instructions perfectly. Choose a lamb, slaughter it and put its blood upon your doorposts so that when The Lord passes thru Egypt He will see that you are 'covered by the blood of the lamb' and He will Passover your home.
They did this and experienced God's gracious Passover for the first time. This Passover freed them from slavery because Pharoah let them go. This Passover saved their lives. This Passover gave them hope. Israel left Egypt and headed towards The Promised Land. They would celebrate this Passover every year (any still do) to remember what God did for them.
Likewise, you and I can have our sinfulness 'Passed Over' when we ask God to forgive our sins and as we follow Jesus as our Lord and Savior. He shed His Blood for us so that we could be 'covered' by it just like those Israelite homes back in Egypt. He gave a 'once for all time' sacrifice of His Own Life so that we could be right with God.
Here are a few verses to read that show that Jesus is perfect, sinless Lamb of God.
1 Corinthians 5:17, John 1:29, John 19:36, Isaiah 53:7, 1 Peter 1:19
Did you know Jesus did this for you? The Israelites celebrated Passover once per year...we should celebrate it every moment. Have you asked God to cover your sins with the sacrificial blood of Jesus?