7 Do you look at things according to the outward appearance? If anyone is convinced in himself that he is Christ’s, let him again consider this in himself, that just as he is Christ’s, even so we are Christ’s.
8 For even if I should boast somewhat more about our authority, which the Lord gave us for edification and not for your destruction, I shall not be ashamed—
9 lest I seem to terrify you by letters.
10 “For his letters,” they say, “are weighty and powerful, but his bodily presence is weak, and his speech contemptible.”
11 Let such a person consider this, that what we are in word by letters when we are absent, such we will also be in deed when we are present.
12 For we dare not class ourselves or compare ourselves with those who commend themselves. But they, measuring themselves by themselves, and comparing themselves among themselves, are not wise.
13 We, however, will not boast beyond measure, but within the limits of the sphere which God appointed us—a sphere which especially includes you.
14 For we are not overextending ourselves (as though our authority did not extend to you), for it was to you that we came with the gospel of Christ;
15 not boasting of things beyond measure, that is, in other men’s labors, but having hope, that as your faith is increased, we shall be greatly enlarged by you in our sphere,
16 to preach the gospel in the regions beyond you, and not to boast in another man’s sphere of accomplishment.
17 But “he who glories, let him glory in the Lord.”
18 For not he who commends himself is approved, but whom the Lord commends.
edification (v.8) means “building up,” while destruction means “tearing down.”
Williams has an interesting take (below) which I don’t know if I entirely agree with in this context, but it bears consideration.
“Authority” (v.8), i.e., his power to inflict sickness or death. The power was real, for when exercised, as in the case of Elymas [Acts 13:8-11], it was effective; and so the Apostle did not fear to be put to shame as he would have been if nothing followed upon his imprecation (v.15). — Williams, page 906.
Don’t go by “outward appearance,” says the apostle (v.7). “If a man trust to himself that he is Christ’s, let him think again, that Paul is Christ’s too—and with greater evidence to substantiate his claim. — Stam, page 194.
In verse 12, when Paul wrote “we dare not class ourselves or compare ourselves with those … ” I think he was being a little sarcastic. Those men were big shots, they had the recommendations, and their appearance and words, unlike Paul’s, were impressive. But Paul wasn’t about to attempt to play their game. God had appointed him to his role, and that’s the directions he would continue to follow. He restates this in verses 17-18.
Why always compare ourselves with others? (v.12). What matters is that the best of us “come short of the glory of God” (Romans 3:23). It is “not wise” to compare ourselves with others for then, assuredly, we have taken our eyes off God.
It will be remembered that there was great rivalry among the Corinthian believers to promote the leaders they preferred. The really serious thing, however, was that some Judaizers and legalizers had infiltrated their ranks, questioning the apostleship of Paul, whom God had so mightily used to found the great church at Corinth.
These Judaizers came with recommendations from the Messianic Church in Jerusalem and asked, in effect, “How can Paul claim to be an apostle of Christ? Christ had twelve apostles when He was on earth, and Paul was not one of them.” — Stam, page 195.