The apostle Paul began this epistle as he did his others by identifying himself and a fellow worker known to the readers. Then he identified and described the recipients of the letter and greeted them with a benediction. This is the most extensive elaboration of an address that we have in Paul's letters.
1:1 Paul's description of himself as one whom God had called to be an apostle of Jesus Christ reminded his original readers of his privilege and authority (cf. Rom. 1:1). The idea of authority received added strength from the reference to the will of God (cf. 2 Cor. 1:1; Eph. 1:1; Col. 1:1; 2 Tim. 1:1).
Sosthenes was probably the same Sosthenes who was the ruler of the synagogue in Corinth (Acts 18:17). He was with Paul in Ephesus when Paul penned this epistle. Though Luke did not record his conversion in the Book of Acts, Sosthenes quite clearly became a believer, assuming this was the same man. Probably he was the same man, and Paul referred to him because the Corinthians knew him well.
1:2 Paul frequently referred to all the Christians in a particular locality as the church of God in that place (cf. 11:16). However to the Corinthian church, where party spirit was a problem, this reminder focused on the church's true Lord. There may or may not have been more than one house-church in Corinth at this time. God had set the Corinthians apart to be His holy people by uniting them with Him through faith in His Son. "Sanctified"may be a metaphor for conversion (cf. v. 30; 6:11). They were saints by divine calling. The Corinthians were not saintly in their conduct, as this letter makes clear. Perhaps Paul mentioned their saintly calling to inspire them to be more saintly in their conduct.11
"Paul understands Christian ethics in terms of becoming what you are,' a perspective that emerges in 1 Corinthians in a number of ways. . . .
"Perhaps the single greatest theological contribution of our letter to the Christian faith is Paul's understanding of the nature of the church, especially in its local expression. If the gospel itself is at stake in the Corinthians' theology and behavior, so also is its visible expression in the local community of redeemed people. The net result is more teaching on the church here than in any of Paul's letters."12
The saints in other places are probably those in churches in other places some of whom had come to the Savior through the witness of Christians other than Paul. This seems more likely than that they were just Paul's converts near Corinth (cf. 2 Cor. 1:1; Rom. 16:1). This seems probable in view of "every place"(NASB) or "everywhere"(NIV) and in view of how this verse ends. Paul evidently wanted his readers to remember that they were part of a large body of believers (cf. 12:12); they were not the only church. They needed to fit into the family of God harmoniously rather than being a rebel congregation.
Calling on the name of Christ means to confess faith in Him, to worship and pray to Him (cf. Rom. 10:13-14).
1:3 This greeting is characteristically Christian (cf. Rom. 1:7; 2 Cor. 1:2; Gal. 1:3). It sums up Paul's whole theological outlook.
