Galatians 1:2

He writeth not only in his own name, but in the name of all those other Christians that were with him in the place where he now was (whether Rome or Corinth, or some other place, is uncertain); with whose consent and privity probably he wrote, possibly at their instigation, and whose common consent in that doctrine of faith which he handleth, (as well as in other things about which he writeth), he here declareth. Some think that the apostle forbears the term saints, or sanctified in Christ Jesus, & c., commonly used in his other Epistles, because of that apostacy for which he designed to reprove them; but it is implied in the term churches. Galatia was a large country, and had in it many famous cities; it was neither wholly Christian, nor yet such as to the major part; but there were in it several particular congregations of Christians, which he calleth churches; every congregation of Christians using to meet together to worship God, being a church, a particular church, though all such congregations make up but one universal visible church. Nor, being guilty of no idolatry, though corrupted in some particular points of doctrine, and those of moment, doth the apostle deny them the name of churches, though he sharply rebuketh them for their errors.