John Gill Bible Commentary

And if Satan cast out Satan,.... That is, if Satan, the same with Beelzebub, casts out the rest of the Satans, or other devils, of which he is the prince and head, he is divided against himself; he acts contrary to his own interest, which is to keep possession of the bodies and souls of men; and consequently it must, in course, be subversive of his power and dominion: how shall then his kingdom stand? he will never be able to maintain his authority, and keep up the show of a government, as he does: for these words suggest, that there is a form of government among the devils, who are united in one body, under one head; and whose unity and concord are their greatest strength, as in all other governments. Our Lord's argument, and which is his first, for others follow, is, that since Satan, who is so cunning and crafty, can never be thought to act such an opposite part to himself, subversive of his kingdom and government; and which would give so much credit to Christ, and serve so much to strengthen his interest, as to assist him in the casting out of devils; the weakness, and maliciousness of such a suggestion, must be clear and evident to all.