1 Corinthians 9:2

Unto others. That is, others not at Corinth, who had not been converted under Paul’s ministry. These might doubt that Paul had been sent of God to preach the gospel, but surely his brethren at Corinth could not entertain any such doubt. He had worked among them for a long time, and they had had abundant opportunity to become acquainted with him and to see how successful his efforts had been. They had more than sufficient evidence that he had been sent to do a great work for God.

Seal. That is, the certificate of authentication. Paul emphatically declares that the existence of the church members in Corinth, the very ones who were indulging in doubt about his right to be called an apostle, was absolute confirmation of his claim that he was an apostle. Their conversion could not have been brought about by man. It was the work of God. It was evidence that God was with His servant and had indeed sent him.

God uses His servants as a skilled artisan uses his tools. They are the means in His hands for accomplishing His purposes among men. As the carpenter uses various tools in the making of a piece of beautiful furniture, and the finished article is recognized as a product of his hand, so the Lord uses His workers on earth to fashion into trophies of His grace, men and women lost in sin. The carpenter knows his own tools and uses them skillfully; so the Lord knows His servants, and under His leadership they are empowered to win men for the kingdom. This success in winning men for the Lord indicates His acceptance of their service, and establishes their status as His witnesses.