The people who were there complain that the firefighters were not called to spray water on the houses that were not burning, but to extinguish the fire in the house that is being consumed. It is doubtful that we will be able to do anything to save it. However, as long as the fire has not spread to the other houses, it is possible to protect them, and that is why we are spraying water upon them. It is the same with regards to the answer given to the wicked son. If a child arises and begins to speak heresy, before we try to straighten his views, we must take care of all the other children, to spray water upon them.
Water is Torah.
First, we must strengthen the other children and innoculate them in order that they should also not be burned by the fire of heresy. Moreover, the verse used to answer the wicked son is the same verse used to answer the simple son who does not know what to ask. Indeed, in the Torah this verse is used explicitly in reference to the simple one. The reason is that when the wicked son asks his question the fire of heresy has already taken hold of him, and we must first address ourselves to the children who have not been infected as yet.