The charge of walking after the flesh is one that needs interpretation. In a general way it means that Paul was a worldly, and not a spiritual, man; and that the key to his character and conduct--even in his relations with Churches--was to be sought in his private and personal interests. What this would mean in any particular case would depend upon the circumstances. It might mean that he was actuated by avarice, and, in spite of pretences to be disinterested, was ruled at bottom by the idea of what would pay; or it might mean--and in this place probably does mean--that he had an undue regard for the opinion of others, and acted with feeble inconsistency in his efforts to please them. A man of whom either of these things could be truly said would be without spiritual authority, and it was to discredit the Apostle in the Church that the vague and damaging charge was made.
He certainly shows no want of courage in meeting it. That he walks _in_ the flesh, he cannot deny. He is a human being, wearing the weak nature, and all its maladies are incident to him. As far as that nature goes, it is as possible that he, as that any man, should be ruled by its love of ease or popularity; or, on the other hand, should be overcome by timidity, and shrink from difficult duties. But he denies that this is his case. He spends his life _in_ this nature, with all its capacity for unworthy conduct; but in his Christian warfare he is not ruled by it--he has conquered it, and it has no power over him at all. "I was with you," he wrote in the First Epistle, "with weakness and fear and much trembling"; but "my speech and my preaching were ... with demonstration of the Spirit and of power." This is practically what he says here, and what must be said by every _man_ who undertakes to do anything for _God_. No one can be half so well aware as he, if he is sincere at all, of the immense contrast between the nature in which he lives and the service to which he is called. None of his enemies can know so well as he the utter earthenness of the vessel in which the heavenly treasure is deposited. But the very meaning of a divine call is that a man is made master of this weakness, and through whatever pain and self-repression can disregard it for his work's sake. With some men timidity _is_ the great trial: for them, it is the flesh. They are afraid to declare the whole counsel of God; or they are afraid of some class, or of some particular person: they are brave with a pen perhaps, or in a pulpit, or surrounded by sympathising spectators; but it is not in them to be brave alone, and to find in the Spirit a courage and authority which overbear the weakness of the flesh. From all such timidity, as an influence affecting his apostolic work, Paul can pronounce himself free. Like Jeremiah (Jer. i. 6-8) and Ezekiel (Ezek. ii. 6-8), he is naturally capable, but spiritually incapable of it. He is full of might by the Spirit of the Lord: and when he takes the field in the Lord's service, the flesh is as though it were not. Since the expression ἐν σαρκὶ περιπατοῦντες refers to the whole of the Apostle's life, it seems natural to take στρατευόμεθα as referring to the whole of his ministry, and not solely to his present campaign against the Corinthians. It is of his apostolic labours in general--of course including that which lay immediately before him--that he says: "The weapons of our warfare are not of the flesh, but mighty before God[82] to the casting down of strong holds."
Nobody but an evangelist could have written this sentence. Paul knew from experience that men fortify themselves against God: they try to find impregnable positions in which they may defy Him, and live their own life. Human nature, when God is announced to speak, instinctively puts itself on its guard; and you cannot pass that guard, as Paul was well aware, with weapons furnished by the flesh. The weapons need to be divinely strong; mighty in God's sight, for God's service, with God's own might. There is an answer in this to many of the questions that are being asked at present about methods of evangelising; where the divinely powerful weapons are found, such questions give no trouble. No man who has ever had a direct and unmistakable blessing on his work as an evangelist has ever enlisted "the flesh" in God's service. No such man has ever seen, or said, that learning, eloquence, or art in the preacher; or bribes of any sort to the hearer; or approaches to the "strong holds," constructed of amusements, lectures, concerts, and so forth, were of the very slightest value. He who knows anything about the matter knows that it is a life-and-death interest which is at stake when the soul comes face to face with the claims and the mercy of God; and that the preacher who has not the hardihood to represent it as such will not be listened to, and should not be. Paul was armed with this tremendous sense of what the Gospel was--the immensity of grace in it, the awfulness of judgment; and it was this which gave him his power, and lifted him above the arts, the wisdom, and the timidity of the flesh. A man will hold his own against anything but this. He will parley with any weapon flesh can fashion or wield; this is the only one to which he surrenders.