When the children of Israel were about to exit Egypt, it was the blood placed on the doorpost and the lintel of believers that's saved that household from destruction.
And when the Jews entered into the Promised Land, it was a red cord hanging from the window of Rahab the Harlot that kept her household from being destroyed.
Both of these instances signify to us the importance of the blood of Christ covering the believer. When the Judgment of God Falls, it is the blood of which delivers us from destruction.
It is as the song writer said, Christ Our Redeemer died on the cross, died for the sinner, paid all his due. Sprinkle your soul with the blood of the Lamb, and I will pass, will pass over you. When I see the blood, when I see the blood, when I see the blood, I will pass, I will pass over you.