How does a church differ from a group of Christians?
Definition of the Church:
At the Council of Constantinople of 381, the Fathers referred to the “one, holy, universal, apostolic church”. This is sometimes referred to as the Four Marks of the Church. Dever discusses these in The Church, chapter 2.
Lutherans define the church as follows in the Augsburg Confession, article 7:
The Church is the congregation of saints, in which the Gospel is rightly taught and the Sacraments are rightly administered.
Calvin defines the church as follows:
Hence the form of the Church appears and stands forth conspicuous to our view. Wherever we see the word of God sincerely preached and heard, wherever we see the sacraments administered according to the institution of Christ, there we cannot have any doubt that the Church of God has some existence.
John Calvin, Institutes of the Christian Religion, 4.1.9.
Dever sees two basic marks of the church:
These two marks are right preaching of the Word of God and the right administration of the baptism and the Lord’s Supper….The first mark is the fountain of God’s truth that gives life to his people, and the second is the lovely vessel to contain and display this glorious work. The church is generated by the right preaching of the Word. The church is distinguished and contained by the right administration of baptism and the Lord’s Supper (21).