How were the Israelites supposed to cook and eat the Passover lamb?
The Passover lamb was to be eaten that night roasted with fire. It was not to be eaten raw or boiled in water, but roasted with fire, a method signifying judgment. They were to consume its flesh in the night, wholly roasted, not raw nor sodden with water, for the fire indicated the judgment Christ would endure.
Les explains that after the lamb was kept up and proved for three days, and found whole, they could kill it for the Passover sacrifice. Then, as verse 7 says, they were to take the blood and strike it on the two side posts and on the upper doorpost of the houses wherein they would eat it. Verse 8 says they were to eat the flesh in that night, roasted with fire. Les notes they were not to eat it raw, nor sodden at all, or boiled in water, but it was to be roasted with fire. He sees the fire as indicative of judgment, just as Christ went through the fires of judgment as He hung on the cross to bring about our salvation. The Passover lamb was not to be fixed any other way but this which indicated a judgment.
And they shall eat the flesh in that night, roast with fire, and unleavened bread; and with bitter herbs they shall eat it.
Eat not of it raw, nor sodden at all with water, but roast with fire; his head with his legs, and with the purtenance thereof.