John Chrysostom — as excerpted in the Catena Aurea on Luke 11:17-20

“(ubi sup.) He did not answer them from the Scriptures, since they gave no heed to them, explaining them away falsely; but he answers them from things of every day occurrence. For a house and a city if it be divided is quickly scattered to nothing; and likewise a kingdom, than which nothing is stronger. For the harmony of the inhabitants maintains houses and kingdoms. If then, says He, I cast out devils by means of a devil, there is dissension among them, and their power perishes. Hence He adds, But if Satan be divided against himself, how shall he stand? For Satan resists not himself, nor hurts his soldiers, but rather strengthens his kingdom. It is then by Divine power alone that I crush Satan under my feet.”