Luke 11:14-23 (ESV)
Now he was casting out a demon that was mute. When the demon had gone out, the mute man spoke, and the people marveled.  But some of them said, "He casts out demons by Beelze-bul, the prince of demons,"  while others, to test him, kept seeking from him a sign from heaven.  But he, knowing their thoughts, said to them, "Every kingdom divided against itself is laid waste, and a divided household falls.  And if Satan also is divided against himself, how will his kingdom stand? For you say that I cast out demons by Beelzebul.  And if I cast out demons by Beelzebul, by whom do your sons cast them out? Therefore they will be your judges.  But if it is by the finger of God that I cast out demons, then the kingdom of God has come upon you.  When a strong man, fully armed, guards his own palace, his goods are safe;  but when one stronger than he attacks him and overcomes him, he takes away his armor in which he trusted and divides his spoil.  Whoever is not with me is against me, and whoever does not gather with me scatters.
Beelzebul, Lord of the Flies, is how it translates, meaning king of the dung hill where the flies swarm. Pretty picture, scripture is so graphic when you understand what it is saying. It makes use of some rather crude metaphors, and harsh language when it all comes down to it. I suppose that is why I like it so much.
The Pharisees are trying to say that Jesus is casting out demons with magic, black arts, and so on. Jesus responds that this is impossible since then Satan would have to be divided against himself, he would be fighting those that are supposed to be helping him in his purposes. He responds that it is by the finger of God, alluding to what the priests of Pharoh had said to him concerning the plagues Moses brought down on the Egyptians. I always find it odd, that they believed in the God but did not trust him. In any case, Jesus artfully throws it all back in their faces, as the Jews themselves had exorcists.
Then he makes it clear, there is no middle ground, you are either for Jesus or against him. Those who do not gather with him will scatter. Jesus is the stronger man, he comes in he will bind the strong man who has power over this world. He will divide his spoil. And so he does, and so he has.