What does Matthew 12:26 mean?

Jesus stands accused by the Pharisees of casting out demons by Beelzebul—in other words, by using the power of Satan (Matthew 12:22–24). These men are so hardened against God that they refuse to accept the obvious (John 5:39–40). Jesus' critics make no effort to claim His work here was a trick or a lie. They know, for a fact, that it's supernatural. What they refuse to accept is that it's godly—since that would mean their traditions and legalism are wrong (Matthew 12:1–8). To explain away the miracle, they need an alternative excuse for Jesus' undeniable power over demons This is the best they can come up with.

Jesus has begun to answer the charge. His first rebuttal is that no nation, city, or even household that is divided against itself can stand. That would be civil war, and the "kingdom" would fall (Matthew 12:25). Now Jesus applies that idea to the charge against Him. Satan sends demons out into the world to do his work. If Satan then casts those same demons out of the ones they have been sent to oppress, Satan would be divided against himself. Jesus asks, "How will Satan's kingdom stand?"

Jesus' point is that the idea is absurd. Satan would not go to war against himself.