Adam Clarke on Mark 9:25

I charge thee - Considerable emphasis should be laid on the pronoun: - Thou didst resist the command of my disciples, now I command thee to come out. If this had been only a natural disease, for instance the epilepsy, as some have argued, could our Lord have addressed it, with any propriety, as he has done here: Thou deaf and dumb spirit, come out of him, and enter no more into him? Is the doctrine of demoniacal influence false? If so, Jesus took the most direct method to perpetuate the belief of that falsity, by accommodating himself so completely to the deceived vulgar. But this was impossible; therefore the doctrine of demoniacal influence is a true doctrine, otherwise Christ would never have given it the least countenance or support.