J. N. Darby

Christ has overcome, and therefore we have only to resist the devil who will flee. If we resist him, he knows that he has met Christ who has all strength against him, for He has vanquished him. The devil can never touch Christ in you - only the flesh; so, if there is a fall, it is a proof you were walking in the flesh. "We wrestle not against flesh and blood," etc. The contrast here is between the conflict with men that Joshua led the children of Israel against (flesh and blood as man, not sinful flesh, is meant here). Now we are not fighting with men, but we are Christians fighting with all these mighty beings, whose subtlety we are apt not to detect because they are so elevated - "against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickednesses in the heavenlies."