We may say, indeed, that faithfulness to Peter himself required it. The strong commendation with which his noble confession has been greeted, instead of making him humble, as it ought to have done, inasmuch as it reminded him that it was not of himself but from above he had the power to make it, seems to have made him over-confident, trustful to that very flesh and blood to which he had been assured he was, in regard to that confession, in no wise indebted. It was therefore necessary that the warm commendation accorded to the strength of his faith should be balanced by an equally strong condemnation of his unbelief. But there is more than this to be said. Christ is looking at Peter, and speaking to Peter; but he recognises another, whom He names and whom in the first place He addresses: "Get thee behind Me, Satan." He recognises the same old enemy, with the same old weapon of assault: for it is the same temptation as that which formed the climax of the conflict in the wilderness, a temptation to prosecute His work by methods which would spare Him the awful agony of the cross. The devil had departed from Him then; but only, as we were informed, "for a season"; and there are frequent indications in the subsequent history that at critical times the great adversary took opportunities of renewing the old temptation. This is one of these occasions. Let us by all means bear in mind that our Lord was true man--that He was "compassed with infirmity," that He was "tempted in all points like as we are," though ever without sin; let us not imagine, then, that His human soul was always on so serene a height that the words of one who loved Him and whom He loved so much would have no effect on Him. It was hard enough for Him to face the awful darkness, without having this new stumbling-block set in His path. It is a real temptation, and a most dangerous one; He may not therefore tamper with it for a moment: He may not allow His affection for His true disciple to blind Him to the real source of it; He must realise with whom He has to deal; He must behind the love of the apostle recognise the malice of the evil one, who is using him as his instrument; accordingly, with His face set as a flint, with His whole being braced for resistance, so that not a hair's-breadth shall be yielded, He says: "Get thee behind Me, Satan: thou art a stumbling-block unto Me" (R.V.)--words which clearly indicate that He had recognised the danger, and summoned the resources of His faith and obedience to put the stumbling-block away.
"Resist the devil, and he will flee from you." We may be sure, therefore, that so soon as the energetic words were spoken _he_ was gone: the stumbling-block was out of the way. The words which follow may therefore be regarded as spoken to Peter himself, to bring to his own consciousness the difference between the heavenly faith which had come by revelation from above, and the earthly doubt and denial, which was evidently not of God, though so natural to flesh and blood: "Thou mindest not the things of God, but the things of men" (R.V.).
Thus once more the Christ of God takes up the cross of man. In doing so He not only sets aside the protest, uttered or unexpressed, of His disciples' hearts; but He tells them plainly that they too must take the same dark path if they would follow Him: "Then said Jesus unto His disciples, If any man will come after Me, let him deny himself, and take up his cross, and follow Me." So He tests them to the uttermost. He withdraws nothing He has said about the blessedness of those who welcome the kingdom of heaven; but the time has come to put the necessary condition in its strongest light, so that, if they still follow, it will be not blindly, but with eyes fully open to all that it involves. He has given hints before of the stringency of the Divine requirement; He has spoken of the strait gate and the narrow way; now He goes to the very heart of that hard matter, and unfolds the innermost secret of the kingdom of heaven. "Let him deny himself:" here is the pivot of all--the _crux_.