"And the blood shall be to you for a token upon the houses where ye are: and when I see the blood, I will pass over you, and the plague shall not be upon you to destroy you, when I smite the land of Egypt."

                            -Exodus 12:13 

Because Pharaoh had refused to let the Israelites go free after 9 plagues, God had to use extreme measures and take the lives of all the first-born. It didn't matter if it was Pharaoh's son, or the first-born of a prisoner in the dungeon; they all had to die (v. 29). However, God made a provision for the Israelites to be saved: through the blood of a spotless lamb. Each family was required to take a lamb, slay it, and then use its blood to mark their door post. When God saw that the blood was applied to that families home, he would not allow the death angel to enter into it and they would be saved (v. 23).

Just like the Egyptians failed to heed God's command, mankind has rejected the Word of God and instead has followed after a sinful lifestyle. As a result, "the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men..." (Romans 1:18) But because He is longsuffering toward us and desires that all might be saved (II Peter 3:9), God has provided a way for us to escape the coming "day of wrath" (Romans 2:5), in which judgment will be poured out upon mankind: through His Son Jesus Christ. Through His blood, we can have forgiveness of sins, and when God sees that blood applied to our hearts, He will know that we are forgiven. Instead of being objects of His wrath, we can now be the objects of His grace and mercy. Not because of our good works; but because of the blood.

What can wash away my sin?
Nothing but the blood of Jesus.
What can make me whole again?
Nothing but the blood of Jesus.

Oh, precious is that flow,
That makes me white as snow!
No other fount I know, 
Nothing but the blood of Jesus.*

*Nothing But the Blood - Rev. Robert Lowery