‘Seeing that you seek a proof of Christ that speaks in me; who to you-ward is not weak, but is powerful in you, for he was crucified through weakness, yet he lives through the power of God. For we also are weak in him, but we shall live with him through the power of God toward you.'
His firm and severe attitude will be because they seek a proof that Christ is speaking in him. So he will follow their criterion. He will come powerfully, and not in humility and meekness as he had before. They claim that Christ is not weak towards them but is powerful in them. That is their justification for their attitude. And in a sense, as long as they are His, it is true, for although He was crucified in weakness (let them note that), yet He lives through the power of God. But they fail to see that the One Who reveals His power within men does so through ‘crucifying' them. It is by dying with Him continually that they experience His power. (Which is why he will now query whether Christ really is in them - 2 Corinthians 13:5).
Well, they should consider that Paul is ‘in Him' and that is why he has been like Christ, not only through outward manifestations but in every way. In Him he has, like Jesus Christ, been meek and lowly and has suffered. And through that God's power has been revealed, as it was through the cross, as many have responded to God's saving power. But now, contrary to his usual attitude, he will ‘live with Him through the power of God' towards them. They will be made to recognise that Christ is with him in the power of God by how he is among them. If they reject lowliness and meekness they will experience the power they desire to see, the very power of God manifested, but in judgment. (This contrast is needed, although some see ‘towards you' as meaning ‘in your service'. But the question must be whether this would answer the proof that they are seeking, and fit in with the connection with ‘I will not spare').
What the Corinthians in their folly constantly ignored was the weakness of Christ, the ‘sufferings of Christ' through which His work went forward and will go forward, as Paul has constantly demonstrated throughout the letter (2 Corinthians 1:5 and often). It is through that that His power is most effectively revealed and effected. It is the ‘word of the cross' that is the true power of God, it is Jesus Christ as the crucified One Who must be proclaimed (1 Corinthians 1:18; 1 Corinthians 2:2). They rather boast in powerful manifestations, concentrating only on His power in the resurrection, a kind of spiritual infusion. They refuse to see that God works powerfully through weakness, and that that is how His work is accomplished in us all, through our dying with Christ that we might live with Him. (How we are all prone to overlook this). Well if that is how they want it they shall have it, they will see the power of God at work.
We do not know exactly what Paul has in mind. It would suggest that like Peter before him (Acts 5:1-11) he is aware that God will act in judgment at his word. Possibly he also bears in mind 1 Corinthians 11:30 and has the confidence that God will act in the same way towards those who bring judgment on themselves by their behaviour towards His chosen Apostle. For if the whole church is against him internal church discipline would not work. (Although we would probably be right to assume that a core is still with him, including some of the leadership). What they will need is to see God's active judgment directed at them. They want to know whether he brings the word of Christ? Well, if they do not repent and become different, they soon will. And it will be their own fault because it is they who have demanded it.