Moses calls the elders of Israel and gives them the instructions. Draw out a lamb — one per household, or share with a neighbor if the household is small. Slaughter it at twilight. Take the blood and, with a bunch of hyssop, mark the lintel and the two doorposts.
Then: none of you shall go out from the door of your house until morning. The destroyer is passing through Egypt. When he sees the blood on the doorposts, he will pass over. He will not enter. He will not strike the house.
The blood is not hidden — it is applied to the outside of the door, visible to anyone who passes. Israel is asked to make itself known: to mark its household publicly as belonging to God on the night when the most fearful judgment passes through the land.
The elders of Israel went and did as Moses commanded. They bowed their heads and worshipped. And they did exactly as God had instructed — not a detail altered.
