The Reformation made the gospel, not ecclesiastical organizations, the test of the true church. Yet the Reformers, particularly in the Calvinistic churches sought biblical standards for the organization of the church.
Three marks were defined in distinguishing a true church of Christ: true preaching of the Word; proper observance of the sacraments; faithful exercise of church discipline.
– Edmund Clowney, The Church: Contours in Christian Theology, copyright 1988, page 101