What does Matthew 12:27 mean?

Jesus is answering an accusation made against Him by the Pharisees. They have claimed His impressive ability to cast out demons comes from Satan, whom they call Beelzebul (Matthew 12:22–24). Jesus' first counterargument is that if this were true, it would mean that Satan was casting out his own demons. He would be in a war against himself, and his kingdom would fall. In other words, the idea itself is foolish (Matthew 12:25–26).

Now Jesus offers a second rebuttal: By whom do the "sons"—in this context, meaning disciples or associates—of the Pharisees cast out demons? Apparently, some Pharisees in Israel practiced exorcisms, or at least claimed to. One thing that impressed the crowds about Jesus was that His authority over demons was absolute. He cast them out with a single word (Matthew 8:16). Exorcists of the day apparently attempted to use incantations and other elaborate ceremonies to remove demons from people.

Jesus' point, though, is more one of simple logic. An accusation that He cast out demons by the power of Satan could only raise questions about whose power the Pharisees called on to cast out demons. Their foolish accusation could backfire on them and bring their own associates' practices into question. The worse problem with that line of thinking, as Jesus goes on to explain, is what it says about the Pharisee's hard-hearted stubbornness towards God (Matthew 12:32).