1:1 The letter begins like a typical ancient Greco-Roman letter: “[Author] to [recipient], greetings.” Paul describes himself as “an apostle of Christ Jesus” whom God himself has called. This supports Paul’s authority to shepherd the Corinthian church, which is important because in this letter Paul’s shepherding includes much admonishing.

Sosthenes is most likely not Paul’s coauthor but rather Paul’s coworker, present with Paul when he writes this letter. The rest of the letter does not mention Sosthenes, and Paul uses the first person throughout.

1:2 Theologians traditionally distinguish at least four senses of “church”: (1) the universal church is the people of God throughout human history—past, present, and future; (2) the invisible church is all genuine believers currently alive on earth; (3) the visible church is professing believers currently alive on earth (we cannot see the invisible church infallibly, as God does, because what we see inevitably includes some people who wrongly claim to be believers); and (4) a local church is part of the visible church—like “the church of God that is in Corinth.” In the NT, “church” usually refers to local churches. And the term always refers to people who gather together—not to a church building. In Scripture, believers are not said to go to church. Instead, they meet with the church. The church regularly gathers to worship God and edify each other through preaching the Bible, performing baptisms, celebrating the Lord’s Supper, and practicing church discipline.

The NT letters present three tenses of sanctification:

(1)  Past. A believer is sanctified (e.g., Heb. 2:11). This occurs when God sets believers apart for himself at the moment he first gives them spiritual life. Some theologians call this definitive or positional sanctification. This is what Paul means when he describes the church in Corinth as “sanctified in Christ Jesus.” God sanctified them through Jesus’ cross-work. All genuine members of God’s church are holy in this sense. When the NT refers to believers as “holy” or “sanctified,” it usually refers to definitive sanctification.8

(2)  Present. A believer is being sanctified (e.g., 2 Cor. 7:1). This is probably what most Christians today think sanctification is: the progressive, incomplete, lifelong maturing process in which a Christian gradually becomes more holy. In that sense sanctification is distinct from both justification (when God instantaneously declares that a believing sinner is righteous) and glorification (when God gives his people imperishable, immortal bodies). Those systematic-theology categories are valid and important. But in the Bible sanctification does not always refer to progressive sanctification. In the NT letters, it usually refers to definitive sanctification.

(3)  Future. A believer will be sanctified (e.g., 1 Thess. 3:13). This ultimate sanctification corresponds to glorification, when God sets his people apart from sin’s presence and possibility.

Paul describes the Corinthian church as both “sanctified in Christ Jesus” and “called to be saints.” They are already holy, and God calls them to be holy. Saints must live like saints. They must become practically what they already are positionally. This follows the pattern of God’s people in the OT: Israel was holy (e.g., Deut. 7:6), and God required Israel to be holy as well (e.g., Ex. 22:31; Lev. 11:44–45). But, as with Israel, Christians cannot be holy without the one person who embodied and accomplished holiness: Jesus is holy, and Jesus makes his people holy. Holy is what God’s people must strive to be now (however imperfectly) until God consummates his plan to make his people holy.

God called the Corinthian church to be saints together with all other believers. He is not requiring more from the church in Corinth than he requires from any of his people anywhere else. God’s people follow the same Master.

1:3 Paul blesses the recipients and specifies the one who gives the grace and peace. For this part of a letter’s introduction, ancient Greco-Roman letters typically announced chairein (“greetings”). Paul tweaks this with a similar-sounding gospel word: charis (“grace”—here with the sense of God’s favor). Ancient letters also customarily opened with a wish for good health, which Paul seems to parallel here by pronouncing a blessing (v. 3) and thanking God for the Corinthians (vv. 4–9).

1:4–8 Paul provides one reason he regularly thanks God for the Corinthians: God gave them his sustaining grace in Christ Jesus. Verses 5–8 explain what that entails. God sufficiently enriched the Corinthians with grace-gifts for communicating and having insight (on spiritual gifts, cf. comments on 12:1–14:40). Thus God confirmed what Paul testified about Christ to the Corinthians, namely, the gospel. The result of God’s enriching the Corinthians is that they will persevere in the faith now while they wait for Jesus to return. Jesus himself will continue sustaining them to the very end in order that (and with the sure result that) they will be guiltless.

1:9 What Paul exclaims here concludes verses 4–9, especially by supporting verse 8: God—the one who called the Corinthians into fellowship with his Son and enriched them with sustaining grace in Christ Jesus—will faithfully sustain them to the end.