Marks of the Church
The Marks of the Church are those things by which the true church may be recognized in Protestant theology. Three marks are usually enumerated: the preaching of the Word, the administration of the sacraments, and church discipline. The Belgic Confession devotes a chapter (Article 29) to the "Marks of the True Church" and lists them as follows:
The true church can be recognized if it has the following marks: The church engages in the pure preaching of the gospel; it makes use of the pure administration of the sacraments as Christ instituted them; it practices church discipline for correcting faults. In short, it governs itself according to the pure Word of God, rejecting all things contrary to it and holding Jesus Christ as the only Head. By these marks one can be assured of recognizing the true church-- and no one ought to be separated from it.
Louis Berkhof notes that Reformed theologians have differed as to the number of marks: Theodore Beza spoke of only one (preaching), John Calvin and Heinrich Bullinger spoke of two (preaching and sacraments), while Peter Martyr and Zacharias Ursinus spoke of three – preaching, sacraments and discipline. Nevertheless, Edmund Clowney points out that Calvin "included discipline in the proper observance of the sacraments." Albert Mohler calls church discipline the "missing mark" of the church.