John Gill

And if Satan also be divided against himself, how shall his kingdom stand?.... This is the accommodation of the above parables, or proverbial sentences; suggesting, that Satan must be against himself, if what the Pharisees said was true; and consequently, his kingdom and government, could not long subsist: because ye say that I cast out devils through Beelzebub; which is all one as to say, that Satan is divided against himself, which is not reasonable to suppose; See Gill on Mat 12:26 and See Gill on Mar 3:26.