What did the blood on the houses of the Israelites serve as?
The blood of the Passover Lamb served as a token upon the Israelites’ houses. When God saw the blood, He would pass over them, and the plague would not be upon them to destroy them when He smote the land of Egypt.
In Exodus 12:12-13, God instructs Moses and Aaron that He will pass through Egypt that night, smite all the firstborn, and execute judgment against all the gods of Egypt. The blood of the Passover Lamb was to be a token upon the houses where the Israelites were. God promises, “When I see the blood, I will pass over you,” and the plague would not destroy them when He smote Egypt. The teaching then pictures the Israelites who had placed the blood on the door standing inside their little cabins or houses around the table, ready to eat the Passover Lamb. They were not in fear and trepidation but had a calm feeling of security because the blood was their token.
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.