If I be not an apostle unto others, yet doubtless I am to you: for the seal of mine apostleship are ye in the Lord. If I be not an apostle unto others - If there be other Churches which have been founded by other apostles; yet it is not so with you.
The seal of mine apostleship are ye - Your conversion to Christianity is God's seal to my apostleship. Had not God sent me, I could not have profited your souls.
The σφραγις or seal, was a figure cut in a stone, and that set in a ring, by which letters of credence and authority were stamped. The ancients, particularly the Greeks, excelled in this kind of engraving. The cabinets of the curious give ample proof of this; and the moderns contend in vain to rival the perfection of those ancient masters.
In the Lord - The apostle shows that it was by the grace and influence of God alone that he was an apostle, and that they were converted to Christianity.