13:1-6 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. Christ at his crucifixion, appeared as only a weak and helpless man, but his resurrection and life showed his Divine power. So the apostles, how mean and contemptible soever they appeared to the world, yet, as instruments, they manifested the power of God. Let them prove their tempers, conduct, and experience, as gold is assayed or proved by the touchstone. If 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, not disowned by Christ. They ought to know if Christ Jesus was in them, by the influences, graces, and indwelling of his Spirit, by his kingdom set up in their hearts. Let us question our own souls; either we are true Christians, or we are deceivers. Unless Christ be in us by his Spirit, and power of his love, our faith is dead, and we are yet disapproved by our Judge.
3. 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" (2Co 13:5). This disproves the assertion of some that Scripture nowhere asserts the infallibility of its writers when writing it.
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 (2Co 5:11, 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 (2Co 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].