Institutes of the Christian Religion
The second edition of Calvin's Institutes of the Christian Religion in 1539 holds that "the marks of the true church [are] that the Word of God should be preached, and that the sacraments be rightly administered". Later, Calvin developed the theory of the fourfold office of pastor, doctor (or teacher), elder, and deacon, possibly owing to the colleagueship with Martin Bucer and his own experience of leadership in church communities.