Greetings to the Church at Corinth

The qualifications of an apostle are highlighted as Paul writes to the Corinthians as an apostle. There is also a lengthy discussion concerning what is the church and the Greek term Ekklesia as used for the Church in the New Testament.
In summary, the physical local church is a manifestation of the universal church of God in a specific place. It is made up of those who have been set apart by God and are joined together by their faith in Jesus Christ. The members of each local church are saints by this calling and having been set apart. All who call upon the name of the Lord are part of the universal church, under the lordship of Jesus Christ, and have been provided with grace and peace by the Father and the Son.