The lawyers begin to question Amulek. They are apparently using their learning to try to catch Amulek in a contradiction. This would allow them to discredit Amulek, and therefore Alma as well. For the lawyers, this was a reasonable process, for they were defending the status quo against two men who were trying to change it. Because there were two men agreeing, this was a serious threat, and is the reason that the lawyers come out only after Amulek begins. When Alma was speaking he was easy to dismiss.
Amulek understands what they are trying to do. We have the phrase “he perceived their thoughts.” We do not know if that perception came because of his familiarity with them and their tactics, or whether or the Spirit whispered them to Amulek. In either case, he does recognize what they are trying to do. What he does is to call them on the tactic, and to do so publicly. This not only answers the lawyers, but it also answers the public that is gathered with them. By attacking the tactic of the lawyers, Amulek notifies all of the people that there is more going on than a simple case of the lawyers defending the integrity of the city. The public might be very willing to accept the lawyers as their defenders, but when the lawyers are classed as associated with the devil (they lay foundations for him) then the people might think twice about accepting implicitly what the lawyers are saying.