What does 1 Corinthians 1:9 mean?

In this brief opening section, Paul has described the glory of God's grace to us in Christ. In short, it is this: Christ does all the work, and we receive all the benefits. Paul has described his own personal gratitude that God has done this for the Christians in Corinth, people Paul knows well from the time he spent with them.

Paul has written that God has sanctified them in Christ, has made them rich in spiritual gifts, and that God will hold them blameless on the day of the Lord. Now he closes the section with an enormous understatement: God is faithful. The rest of this letter will reveal deep and ugly problems among the church in Corinth, but none of those things will keep God from being faithful, by His grace, to any person who has come to Him through faith in Jesus.

Paul's readers, these troubled Corinthian Christians, were called by God into the fellowship of His own Son Jesus. All Christians are called into that fellowship. This tells us two things about what God intends for us. First, He does not mean to save us and then have us keep our distance until we arrive in eternity. God sees us as being in fellowship, a deep and direct relationship, with Him, with Christ. Second, Paul is emphasizing that all who are in Christ are, by definition, in relationship with each other.

These relationships themselves are a gift. Paul's letter will show, though, that the Corinthians were not valuing, in all cases, the gift of their fellowship with each other in Christ.