The role of the bishop as the guarantor of the faith, the focus of unity, and the guardian against heresy and schism, is one which has a long history. As early as the third century, Cyprian, Bishop of Carthage, wrote to Cornelius, Bishop of Rome, that

In his tract De ecclesiae catholicae unitate, he understood the bishops to be the glue which holds together the universal church. The believer knows he is part of the church because his bishop is part of the unity which forms the whole. By the Middle Ages, perhaps as a result of painful experience, it had come to be accepted in many quarters that the holding episcopal office was by itself no guarantee of orthodoxy. Marsilius of Padua taught that the pope or bishops might possibly be heretics, though he did not state that there had ever been an instance of a heretical pope. The writings of Augustine were prominent amongst the works of the Fathers which were consulted by those who actively sought the reform of the Church. To bishops presented with the presence of heresy in their charges, Augustine was important as a model for the resident bishop who countered heretics by force as well as by argument.