2 Corinthians 1:1

This is the introduction to this epistle, in which we have, I. The inscription; and therein, 1. The person from whom it was sent, namely, Paul, who calls himself an apostle of Jesus Christ by the will of God. The apostleship itself was ordained by Jesus Christ, according to the will of God; and Paul was called to it by Jesus Christ, according to the will of God. He joins Timotheus with himself in writing this epistle; not because he needed his assistance, but that out of the mouth of two witnesses the word might be established; and this dignifying Timothy with the title of brother (either in the common faith, or in the work of the ministry) shows the humility of this great apostle, and his desire to recommend Timothy (though he was then a young man) to the esteem of the Corinthians, and give him a reputation among the churches. 2. The persons to whom this epistle was sent, namely, the church of God at Corinth: and not only to them, but also to all the saints in all Achaia, that is, to all the Christians who lived in the region round about. Note, In Christ Jesus no distinction is made between the inhabitants of city and country; all Achaia stands upon a level in his account. II.

— Matthew Henry's Concise Commentary (public domain)