In the first verse, Paul introduces himself as one who is sent by Jesus Christ, and by the will of God, and adds Sosthenes, who used to be the leader of a synagogue in Corinth. Then, he describes the Corinthian church as those who have been set apart for God in Christ, and have been called by God to be set apart ones with everyone who trusts in the name of Christ, who is the Lord of all saints.
In verse 3, he wishes grace and inner peace upon the church from the Father and Christ, the Son. Then, he begins his thanksgiving for them, which happens whenever he prays about them, because God gave them grace in Christ. This grace caused them to be rich in everything, including speech and knowledge. In addition, they had Paul’s testimony about Christ confirmed within them, so they possess every necessary gift. Furthermore, they are eagerly awaiting the second coming of Christ, who is the One that will confirm them as saints — saints who will be blameless on that day. Finally, Paul promises them that God is faithful, and is the One who called them into a partnership with His Son.