1 Corinthians 9:1

Blessed Paul, in the work of his ministry, not only met with opposition from those without, but discouragement from those within. He was under reproach; false brethren questioned his apostleship, and were very industrious to lessen his character and sink his reputation; particularly here at Corinth, a place to which he had been instrumental in doing much good, and from which he had deserved well; and yet there were those among them who upon these heads created him great uneasiness. Note, It is no strange nor new thing for a minister to meet with very unkind returns for great good-will to a people, and diligent and successful services among them. Some among the Corinthians questioned, if they did not disown, his apostolical character. To their cavils he here answers, and in such a manner as to set forth himself as a remarkable example of that self-denial, for the good of others, which he had been recommending in the former chapter. And, 1. He asserts his apostolical mission and character: Am I not an apostle? Have I not seen Jesus Christ our Lord? To be a witness of his resurrection was one great branch of the apostolical charge. "Now," says Paul, "have not I seen the Lord, though not immediately after his resurrection, yet since his ascent?" See Co1 4:8.

— Matthew Henry's Concise Commentary (public domain)