Jesus shows the logical flaw in the rumour being spread by the scribes. By doing this in the presence of the crowds (Mark 3:20, Mark 3:32), he also defends his ministry and makes it clear to everyone that he is not possessed by Satan. As a result, the scribes will look foolish if they continue arguing that he is a sorcerer, and they will therefore not be able to have him killed as they planned.
23 And he called them to him and said to them in parables, “How can Satan cast out Satan?