Final answer:
The Israelites put blood on the tops of the door frames as a symbol of the Passover sacrifice and for protection.
Step-by-step explanation:
The Israelites put blood on the tops of the door frames as a symbol of the Passover sacrifice. During the last of the ten plagues in Egypt, the Angel of Death would pass over the homes with the blood on the door frames, sparing the lives of the firstborn sons. By marking their houses with blood, the Israelites were following the commandment from Moses to ensure their protection.