In these verses observe,

I.The apostle threatens to be severe against obstinate sinners when he should come to Corinth, having now sent to them a first and second epistle, with proper admonitions and exhortations, in order to reform what was amiss among them. Concerning this we may notice, 1. The caution with which he proceeded in his censures: he was not hasty in using severity, but gave a first and second admonition. So some understand his words (Co2 13:1): This is the third time I am coming to you, referring to his first and second epistles, by which he admonished them, as if he were present with them, though in person he was absent, Co2 13:2. According to this interpretation, these two epistles are the witnesses he means in the first verse, referring rather to the direction of our Saviour (Mat 17:16) concerning the manner how Christians should deal with offenders before they proceed to extremity than to the law of Moses (Deu 17:6; Deu 19:15) for the behaviour of judges in criminal matters. We should go, or send, to our brother, once and again, to tell him of his fault. Thus the apostle had told these Corinthians before, in his former epistle, and now he tells them, or writes to those who heretofore had sinned, and to all others, giving warning unto all before he came in person the third time, to exercise severity against scandalous offenders. Others think that the apostle had designed and prepared for his journey to Corinth twice already, but was providentially hindered, and now informs them of his intentions a third time to come to them. However this be, it is observable that he kept an account how often he endeavoured, and what pains he took with these Corinthians for their good: and we may be sure that an account is kept in heaven, and we must be reckoned with another day for the helps we have had for our souls, and how we have improved them. 2. The threatening itself: That if (or when) he came again (in person) he would not spare obstinate sinners, and such as were impenitent, in their scandalous enormities. He had told them before, he feared God would humble him among them, because he should find some who had sinned and had not repented; and now he declares he would not spare such, but would inflict church-censures upon them, which are thought to have been accompanied in those early times with visible and extraordinary tokens of divine displeasure. Note, Though it is God's gracious method to bear long with sinners, yet he will not bear always; at length he will come, and will not spare those who remain obstinate and impenitent, notwithstanding all his methods to reclaim and reform them.

II.The apostle assigns a reason why he would be thus severe, namely, for a proof of Christ's speaking in him, which they sought after, Co2 13:3. The evidence of his apostleship was necessary for the credit, confirmation, and success, of the gospel he preached; and therefore such as denied this were justly and severely to be censured. It was the design of the false teachers to make the Corinthians call this matter into question, of which yet they had not weak, but strong and mighty proofs (Co2 13:3), notwithstanding the mean figure he made in the world and the contempt which by some was cast upon him. Even as Christ himself was crucified through weakness, or appeared in his crucifixion as a weak and contemptible person, but liveth by the power of God, or in his resurrection and life manifests his divine power (Co2 13:4), so the apostles, how mean and contemptible soever they appeared to the world, did yet, as instruments, manifest the power of God, and particularly the power of his grace, in converting the world to Christianity. And therefore, as a proof to those who among the Corinthians sought a proof of Christ's speaking in the apostle, he puts them upon proving their Christianity (Co2 13:5): Examine yourselves, etc. Hereby he intimates that, if they could prove their own Christianity, this would be a proof of his apostleship; for if they were in the faith, if Jesus Christ was in them, this was a proof that Christ spoke in him, because it was by his ministry that they did believe. He had been not only an instructor, but a father to them. He had begotten them again by the gospel of Christ. Now it could not be imagined that a divine power should go along with his ministrations if he had not his commission from on high. If therefore they could prove themselves not to be reprobates, not to be rejected of Christ, he trusted they would know that he was not a reprobate (Co2 13:6), not disowned by Christ. What the apostle here says of the duty of the Corinthians to examine themselves, etc., with the particular view already mentioned, is applicable to the great duty of all who call themselves Christians, to examine themselves concerning their spiritual state. We should examine whether we be in the faith, because it is a matter in which we may be easily deceived, and wherein a deceit is highly dangerous: we are therefore concerned to prove our own selves, to put the question to our own souls, whether Christ be in us, or not; and Christ is in us, except we be reprobates: so that either we are true Christians or we are great cheats; and what a reproachful thing is it for a man not to know himself, not to know his own mind!

Since ye seek a proof of Christ - The conversion of the Corinthians was to themselves a solid proof that Christ spoke by the apostle; and therefore he could, with great propriety, say that this power of Christ, far from being weak, was mighty among them.

Since ye seek a proof of Christ speaking in me,.... This is the reason why he was determined, that should he come among them, he would not spare them, because they called in question his apostleship, and demanded a proof of it; which, of all men, they had the least reason to do; for they themselves were the seals of his apostleship, and the signs of an apostle had been done among them; they queried whether he was an ambassador of Christ, and was sent by him, and in his name; whether the message he came with was from him, and whether the Gospel he preached was his voice; and particularly whether he had such a power to punish delinquents, as he threatened them with the exercise of; a strange infatuation of the false apostles this, since Christ, who sent him, was with him, and spoke in him, and by him:

which to you-ward, says he,

is not weak, but is mighty in you; the Gospel of Christ, at the first preaching of it to them by him, was the power of God unto salvation to them; and was attended with divers signs and wonders, and gifts of the Holy Ghost; and besides, they had instances of the power of Christ towards them in an awful way, in punishing sinners; as in the delivery of the incestuous person to Satan, which was done by his Spirit being with them when assembled; and by smiting many of them with sickness, diseases, and infirmities, and with death itself, who had sinned, Co1 5:4. Wherefore, seeing after all these instances of the voice and power of Christ in him, they yet questioned his apostolical authority, and sought proof of it; and especially since this was not so much a tempting of him, as a tempting of Christ in him, he was resolved not to spare them.

Since--The reason why he will not spare: Since ye challenge me to give a "proof" that Christ speaks in me. It would be better if ye would "prove your own selves" (Co2 13:5). This disproves the assertion of some that Scripture nowhere asserts the infallibility of its writers when writing it.

which--"who" (Christ).

is not weak--in relation to you, by me and in this very Epistle, in exercising upon you strong discipline.

mighty in you--has given many proofs of His power in miracles, and even in punishing offenders (Co2 5:11, Co2 5:20-21). Ye have no need to put me to the proof in this, as long ago Christ has exhibited great proofs of His power by me among you (Co2 12:12) [GROTIUS]. It is therefore not me, but Christ, whom ye wrong: it is His patience that ye try in despising my admonitions, and derogating from my authority [CALVIN].