The blood is powerful. In the Old Testament; when the children of Israel were in great threat of peril in the eyes of many, God sent instructions for safekeeping. That same safekeeping is available to us now.
They were told to apply blood on the doorposts of their houses and that as a result when the angel of death was sent to kill the firstborn of people and animals and to render helpless the false gods; that they would be passed over.
You see, demons tremble at the blood. They see it spiritually and all you have to do is believe that it covers you like paint and say the blood of Jesus covers me believer. It won’t work for non believers.
READ THE BOOK OF EXODUS for a greater understanding.
Exodus 12: 13, 14
13The blood shall be for a token or sign to you upon [the doorposts of] the houses where you are, [that] when I see the blood, I will pass over you, and no plague shall be upon you to destroy you when I smite the land of Egypt.(C)
14And this day shall be to you for a memorial. You shall keep it as a feast to the Lord throughout your generations, keep it as an ordinance forever.