John Gill Commentary Luke 11:18

"And if Satan also is divided against himself, how shall his kingdom stand? because ye say that I cast out demons by Beelzebub." — Luke 11:18 (ASV)

And if Satan also be divided against himself, how shall
his kingdom stand ?
&c.] 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 you 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 Matthew 12:26) and (See Gill on Mark 3:26).