The final grim struggle came under Diocletian. That very able man tried to re-organise the Empire that he might save it. By 30o Christianity had many adherents, and Diocletian was per suaded that the decadence he was fighting was partly due to this. Hence he began in 3o3 to publish a number of edicts which led to the most bitter of the persecutions. The effort to destroy Christianity continued under his successors, who divided the im perial authority between them. Only in Gaul was there compara tive peace under Constantius Chlorus. When his son Constantine fought for the empire, he relied somewhat on Christian help. His success in 323 led to the enforcement of his own Edict of Milan of 313. By this Christianity was given peace, a peace never afterwards openly broken, save under Julian the Apostate (361 363) who reverted to paganism. With peace came victory. Grad ually paganism died out. The open war had been won by the Church.
During the struggle the Church in her reaction to successive crises had shown clearly that she was an organised society. The duty of unity between Christians was always recognised. Only by official membership of the Church could salvation be secured, and such membership depended upon the authorities of the Church. She was the Body of Christ, mystically but really; and only by union with that Body could a man be united to Christ. We can see this in numerous passages of the New Testament, es pecially in St. John's Gospel and in the Epistles of St. Paul; the same doctrine is prominent in the works of St. Irenaeus, in the Pastor of Hermas, in the writings of Tertullian, and perhaps most clearly in the works of St. Cyprian. It is evidently assumed in the practice of excommunication, the refusal of membership to great sinners, in the importance of Baptism, in the practice of Penance. This unity, moreover, was universal. By councils, by letters, by mutual prayer, the union of all Christian communities was con stantly expressed.
The central authority inevitably acompanying this unity was always found in the pre-eminence of the Roman Church. The details of this authority may be difficult to ascertain from the evi dence. But from the various controversies, especially from those in which the Roman authority was questioned, it seems plain to the writer that the community of Rome was the leading one of the Christian Church, and that only by union with it could a man be truly a member of the Church itself ; and, further, that from Apostolic days, each community was ruled by priests, and that among the priests at least mere convenience caused one to be recognised as leader. This one was shortly called the Bishop, and to him the fullness of the priesthood was soon reserved. Thus the leader or bishop of the Roman community was the leader of the Church as a whole.
The heresies and difficulties of the first three centuries made even clearer the duty of unity, and the authority of the Roman bishop. By 30o it is perfectly certain that there was established a hierarchy of bishops, priests and deacons to rule individual communities. Unless we also recognise that these individual com munities were also united to each other by the bond of their common union with Rome, we cannot understand such contro versies as the Montanist, the Quattuor-Deciman, the Novatian, or the discussion on re-baptism, nor can we hope to understand later history and the steady development of Roman authority. We may disbelieve in this unity and in its corollary the authority of Rome, but as historians we must admit that these doctrines were believed from the beginning.
B. The Second Period.—We cannot treat fully of the peace thus established. So far the Church had resisted successfully an openly hostile State which expressly attacked the Christian Reve lation. Now the attack was subtler. As gradually paganism was destroyed, and ultimately made illegal, the temporal rulers, being themselves Christian and accepting the basic Christian principle that God had revealed Himself, tried to intervene in doctrinal disputes. Though the rulers of the Church always saw in this at tempt disloyalty to Christ, this was not realised so clearly by everybody. Consequently the State was able to make the effort, with at times apparent chance of success.
During this period certain developments occurred. Since much of the Imperial effort to assert authority consisted in supporting faulty expressions of Christian doctrine, the Church's resistance led to a clearer understanding and a more definite expression of those doctrines. Thereby moreover the authority of the Church as the sole authentic exponent of Revelation became more mani fest. The great heresies of the period may be divided into three groups. There is first the group which led to discussion of the Trinity and the Incarnation. These heresies are obviously akin.
Arius in trying to simplify the doctrine of the Trinity destroyed it, by denying true divinity to the Second Person. The refutation of this error led naturally to discussion of the Third Person. Once the doctrine of the Trinity was safeguarded discussion easily arose on the Incarnation of the Second Person. Re-action against de nial of any true divinity to Christ led easily to a virtual denial of true humanity. When these heresies, despite State support, were all refuted, not only did the doctrines attacked stand out the clearer, but there was inevitably a surer recognition of the maj esty of the Church, founded by the Incarnate God, His Mystical Body, which spoke in His name and by his authority.