Charles Ellicott Commentary 1 Corinthians 9:2

"If to others I am not an apostle, yet at least I am to you; for the seal of mine apostleship are ye in the Lord." — 1 Corinthians 9:2 (ASV)

If I be not an apostle unto others.—The allusion here is probably to some who may have arrived at Corinth after St. Paul’s departure, and who, not recognizing his Apostleship in relation to themselves, stirred up some of the Corinthians to repudiate it also. So the Apostle says, “Even if I am not an Apostle to these others, I am, in any case, to you; for you yourselves are the very proof and witness—the seal affixed to my appointment to the Apostolate.” The repetition of the words “in the Lord” in both these verses expresses the strong conviction, which is characteristic of the Apostle, that the source of all power and of all success is Christ Himself.