‘For I will pass through the land of Egypt on that night, and will strike all the firstborn in the land of Egypt, both man and beast; and against all the gods of Egypt I will execute judgment: I am the Lord. Now the blood shall be a sign for you on the houses where you are. And when I see the blood, I will pass over you; and the plague shall not be on you to destroy you when I strike the land of Egypt.
The blood of the lamb was a sign to God that the people believed in His provision and protection. Wherever the blood was, there could be no plague.
PRAY ISRAEL AND ALL PEOPLE WILL BELIEVE IN THE PASSOVER LAMB.