But if I cast out devils by the Spirit of God, then the kingdom of God is come unto you. But if I cast out devils by the Spirit of God - Perhaps the Spirit of God is here mentioned by way of opposition to the magical incantations of the Jews; for it is well known that by fumigations and magical washings, they professed to cast out devils. See a case mentioned by Schoettgen on this verse.
Then the kingdom of God - For the destruction of the kingdom of Satan plainly implies the setting up of the kingdom of God.
Is come unto you - Is come unexpectedly upon you. Εφθασεν, from φθανω, to appear suddenly - unexpectedly.
They pretended to be in expectation of the kingdom of God, and consequently of the destruction of the kingdom of Satan. But, by being not prepared to receive Christ in these proofs of his Divine mission, they showed that their expectation was but pretended. They were too carnal to mind spiritual things.