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.

This verse startlingly reveals some things about Satan. Spence said:

Throughout this argument, Jesus assumes the existence of a kingdom of evil, all armed and thoroughly organized to carry out its dread purposes. He concedes, too, in language which admits of no questioning, the existence of a chief of this evil confederacy.[26]

Further, as Boles noted, "It will be noted that Satan here is represented as a real person, not a mere principle of evil."[27]

Now it happened that some of the Pharisees themselves professed to cast out demons, an action which they advocated as holy, helpful, and righteous; and Jesus quickly moved to point out that, judged by their own approval of exorcism, they had already admitted such deeds as he had performed before their very eyes to be of God.

[26] H. D. M. Spence, Pulpit Commentary (Grand Rapids, Michigan: Wm. B. Eerdmans Publishing Company, 1962), Vol. 16, Luke, p. 303.

[27] H. Leo Boles, op. cit., p. 235.