1: 1 — Paul, called to be an apostle of Christ Jesus by the will of God, and our brother Sosthenes,
[T - OL - SD - Gk ]

We cannot be certain how many, and how many of the extant, letters Paul had already written to the churches when he wrote 1 Cor. Given Paul's pastoral heart, it would not be surprising if it had been considerable (though in all, only some are recognized as having been preserved in the canon of Scripture). In all of those that have been preserved Paul follows the convention of letter writing of the time by identifying himself as the author of the letter. As happens elsewhere in his letters Paul most frequently identifies himself as an "apostle of Christ." Almost always he immediately qualifies this with the fact that he has been "called to be" so or "by the will of God," both meaning essentially the same thing, i.e., he did not an apostle by self-appointment (See Paul's Self-Identity). Here in this letter, where he is addressing a situation in which his authority is being called into question, it is particularly appropriate that he should identify himself "an apostle . . . by the will of God."

He also names "our brother Sosthenes" in this heading. Sosthenes may not be an apostle but he is ho adelphos, literally, "the brother." The idea of calling someone who is aligned to one's cause 'a brother' is common in many cultures; it was certainly not strange to the Greeks or the Jews. But, as C. K. Barrett observes, "[t]he Gospel supplied a new basis in reality, and generated warmth of feeling, but it did not create a wholly new vocabulary."1

Elsewhere the inclusion of another name(s) at this point in the letter implies their identification with the content and co-authorship of the letter. This is unlikely to be so in this case. Sosthenes does not appear again in the letter, and his absence in the letter's conclusion is strong evidence of this. Still the inclusion of Sosthenes's name here may not be insignificant. The name Sosthenes appears elsewhere only in Acts 18:17. Back during the days of Paul's first visit to Corinth the Jews in the city had made "a united attack on Paul" and brought a case against him before Gallio the proconsul. When Gallio dismissed their quarrel as none of his business, the Jews took out their frustration by beating up the leader of the synagogue—a man named Sosthenes—right in the proconsul's presence but he did not care. We cannot be certain that the Sosthenes of 1 Cor and the Sosthenes of Acts 18 were the same person, but a good case may be argued for it. Though Sosthenes is not reported to have taken the initiative for starting the attack on Paul, as a leader of the local synagogue he is a very likely suspect. If that was so, his public humiliation must have been particularly stinging. Paul being Paul, it would have been very him to have gone visiting Sosthenes after the ruckus had died down and to minister to him, enemy or no. It is not beyond likelihood that that Sosthenes of Acts had believed in the gospel and became the Sosthenes of 1 Cor. If that was the case, the mention of Sosthenes at the head of the letter may be significant, as Bailey suggests:2

If he is the same man—John Calvin seems certain of it—having served as the head of the synagogue in Corinth, Sosthenes naturally would have known a great deal about the Jewish-Christian members of the Corinthian church and could have provided great help to Paul in the writing of this letter. Regardless of his identity, Sosthenes was most certainly known to the Corinthians, otherwise Paul would not have mentioned him by name. The two of them undoubtedly discussed what to include and what to omit in this critical epistle.

At the same time, by including Sosthenes as a joint sender of the letter, he is saying,

I know that I am a newcomer to your city. Please understand that I am not sitting here in Ephesus in grand isolation from the real world of Corinth and its society, dreaming up criticisms of your theology and ethics. Sosthenes agrees with everything I have to say to you. Keep that in mind as you read. We are together sending you this letter.

If Sosthenes could not be counted as a co-author, he was—if Bailey is right—Paul's very useful advisor in the drafting of the letter.

You may wish to read the following commentaries-expositions:

John Calvin
Matthew Henry