Musar zu Dewarim 7:25

Commandment 428 prohibits the use of any object which has served as part of a pagan cult in any form. The Torah (7,25) states: "You must not covet any of the silver or gold attached to the pagan symbols (which you have been enjoined to burn) to acquire them for yourselves."

The Zohar, commenting on 12,3: ויקחו להם איש ה לבית אבות שה לבית, "They shall each acquire for themselves a lamb per family or a lamb per household," comments that in effect G–d told the Jews to physically get hold of the Egyptians' deity, to keep it locked up for three days and to publicly excecute it on the fourth day. The Egyptians had to witness all this. This was a harder pill for them to swallow than all the other plagues that they had been subjected to previously, and this their idol was afterwards to be roasted on the fire as part of its execution. It was not to be boiled in water because the Torah's command to burn the idols (of the nations we conquered) in fire legislated in Deut. 7,25 would not have been carried out by boiling. If one were to boil the Passover lamb it would be equivalent to hiding it, covering it up, and one could not smell its fragrance. The distinctive smell of its roasting should permeate the house. The reason that it must be roasted whole with its legs and head is to prevent giving the impression that it is alive or that it is a pig, for instance. It must be prepared as food in such a way that everyone notices that it is an Egyptian deity that is being treated in this fashion. The Passover lamb must also not be eaten in a ravenous manner, but at a time when one has almost completed one's meal. No bone may be broken so that the skeleton can be viewed as whole, and its inability to save itself be demonstrated. For all these reasons the Torah speaks about ובאלוההים עשה שפטים "He executed judgments on their deities" (Numbers 33,4).