1 Corinthians 1:2 - Matthew Poole's English Annotations on the Holy Bible

Unto the church of God which is at Corinth; unto those in Corinth who having received the doctrine of the gospel, and owned Jesus Christ as their Saviour, were united in one ecclesiastical body for the worship of God, and communion one with another. Corinth was a famous city in Achaia, (which Achaia was joined to Greece by a neck of land betwixt the Aegean and Ionian Seas), it grew the most famous mart of all Greece. Paul came thither from Athens, Acts 18:1. Crispus, the chief ruler of the synagogue there, believed, upon Paul's preaching; so did many Corinthians, and were baptized, 1 Corinthians 1:9. He stayed there eighteen months, 1 Corinthians 1:11; there Sosthenes (mentioned 1 Corinthians 1:1) was converted; from thence Paul went to Ephesus, 1 Corinthians 1:19. These believers were those here called the church of God at Corinth, to whom he writes this Epistle (as it should seem from 1 Corinthians 16:8) from Ephesus, where Paul stayed three years, Acts 20:31. The members of this church the apostle calleth such as are sanctified in Christ Jesus, called to be saints: whether by the term the apostle meaneth only such as by the preaching of the gospel were separated from the heathens at Corinth, and professed faith in Christ, (as, Acts 15:9, the apostle saith the Gentiles hearts were purified by faith), or such in Corinth as were really regenerated, and had their hearts renewed and changed, is not easy to determine: both of them are saints by calling; the former are called externally by the preaching of the gospel, the other internally and effectually by the operation of the Spirit of grace. It is most probable, that St. Paul intended this Epistle for the whole body of those that professed the Christian religion in Corinth, though in writing of it he had a more special respect to those who were truly sanctified in Christ by the renewing of the Holy Ghost. Nor doth Paul only respect those that lived in Corinth, but he directs his Epistle to all those who in any place of Achaia called upon the name of Jesus Christ, whom he calleth their Lord, and our Lord: which is an eminent place to prove the Divine nature of Christ; he is not only called our Lord, our common Lord, but he is made the object of invocation and Divine worship: and it teacheth us, that none but such as call upon the name of Jesus Christ our Lord, are fit matter for a gospel church; which both excludes such as deny the Godhead of Christ, and such as live without God in the world, without performance of religious homage to God the Father and the Lord Jesus Christ, and owning him as their Lord.