In the face of all the misunderstandings on the part of the world and all the errors which have arisen within Christendom, let us make this point absolutely clear: the task of the church in the world consists uniquely and alone in the preaching of the Word of God and in administering the Sacrament. All other functions which the church as a living organism develops and uses serve only to fulfill this task. All activities which the church can legitimately exercise in the world are by-products of preaching and the Sacraments. Christ had no other purpose in sending His church into the world than preaching and distributing the Sacraments. Only in accomplishing this task is the church recognizable as the church. In addressing this issue of identifying the basic church functions, the Reformation claimed that the marks of the church were the Word and the Sacraments. In these signs, the church could be recognized.
To be sure brotherly love, providing for the poor and the sick, moral discipline, prayer and worship will be present wherever the church is, but a fellowship (congregation) with only these marks is clearly unrecognizable as the church. Brotherly love can be found in the synagogue. The poor and the sick are provided for by modern secular governments. Moral discipline is a part of Buddhist monasteries. Prayer and worship are features of all religions in the world. The Gospel, Baptism, and the Lord’s Supper can be found only in the church. They are the indelible marks of the church.
The moral sensitivities of the natural man are in no way satisfied by the Bible. All the Bible’s moral injunctions can be found in other religions and philosophies. In fact, the moral sensitivity of the natural man finds the Bible offensive, because its central theme is that God accepts sinners and only sinners as righteous.