Albert Barnes Commentary Exodus 12:9

"Eat not of it raw, nor boiled at all with water, but roast with fire; its head with its legs and with the inwards thereof." — Exodus 12:9 (ASV)

Raw - that is, “half-cooked.”

Sodden ... with water - It was probably more common to boil meat than to roast meat; therefore, the regrets expressed by the Israelites for the boiling pots of Egypt.

The purtenance thereof - or its intestines. This verse directs that the lamb should be roasted and placed on the table whole. No bone was to be broken (see Exodus 12:46, and margin reference). The bowels were taken out, washed and then replaced. The Talmud prescribes the form of the oven of earthenware in which the lamb was roasted, open above and below with a grating for the fire. Lambs and sheep are roasted whole in Persia, nearly in the same manner.

This entire consumption of the lamb constitutes one marked difference between the Passover and all other sacrifices, in which either a part or the whole was burned, and thus offered directly to God. The whole substance of the sacrificed lamb was to enter into the substance of the people, the blood only excepted, which was sprinkled as a propitiatory and sacrificial offering.

Another point of subordinate importance is noted. The lamb was slain and the blood sprinkled by the head of each family: no separate priesthood yet existed in Israel; its functions belonged from the beginning to the father of the family. When the priesthood was instituted, the slaying of the lamb still devolved on the heads of families, though the blood was sprinkled on the altar by the priests—an act which essentially belonged to their office.

The typical character of this part of the transaction is clear. Our Lord was offered and His blood shed as an expiatory and propitiatory sacrifice, but His whole Humanity is transfused spiritually and effectually into His Church, an effect which is at once symbolized and assured in holy communion, the Christian Passover.