Charles Ellicott Commentary 1 Corinthians 15:9

"For I am the least of the apostles, that am not meet to be called an apostle, because I persecuted the church of God." — 1 Corinthians 15:9 (ASV)

For I am the least of the apostles.—Paulus Minimus. Here, the mention of his conversion—the thought of what he had been before, what he had become since—leads the Apostle into a digression, occupying this and the next two verses. The two thoughts of his own inherent nothingness and of his greatness by the grace of God are here mingled together in expressions of intense personal feeling.

While he was a persecutor, he had thought that he was acting for the Church of God; he was really persecuting the Church of God. The Christian Church had completely taken the place of the Jewish Church—not merely abolished it, but superseded it.