Musar zu Schemot 12:13

The time to offer this sacrifice is בין הערבים (12,6), during the period when the מנחה prayer which the patriarch Isaac introduced is recited. You are familiar with the deeper significance of the prayer. The requirement to smear some of the blood of that sacrifice on the lintel and doorposts of your houses, [only on the first Passover, the one slaughtered prior to the Exodus] is a symbol of the attribute of מלכות, also displayed by Isaac, known as פתח האהל, "entrance or gateway to the tent." This is the meaning of: והיה הדם לכם לאות על הבתים אשר אתם שם, "The blood will be a sign for you on the houses wherein you are staying” (12,13). The consumption of the meat of the sacrifice, which must take place at night, is an allusion to the attribute לילה, and this is why you must not leave any of it until the morning (12,10). The reason it has to be roasted on the fire (12,9) is that the sacrifice is symbolic of the Heavenly Fire which is known as אש אוכלת, “a consuming fire.” By roasting it on the fire, the power of that אש אוכלת is diminished and the power of all the accusers of the Jewish nation who derive their “fire” from it is weakened. This is another reason why it is forbidden to boil the meat of the sacrifice in water.