Theological aspects. From the theological point of view, the principle was strengthened, which was already present in the first three centuries, according to which the monarchical episcopate corresponded to God’s will, his institution through Jesus Christ and the laying on of hands through the apostles. This theological explanation placed the order of the Christian priesthood in relation to the action of Jesus Christ, so to speak, with his preaching and promises, the Last Supper and the institution of the Eucharist, with the granting of the power to forgive sins, with the election of the disciples, to whom he entrusted the mission and with the sending of the Holy Spirit. The contention that the theological foundation for the origins of the episcopate must be historically traced back to Jesus Christ himself is explained starting from the form of thought, proper to that time, which maintained that what was in place at that time was so since the beginning. With Eusebius of Caesarea Dem. Ev. 4,15,20 a distinction began to be made in the priestly action, the threefold office munus triplex of Christ regal, sacerdotal and prophetic in which the bishops fully participated.
The theological vision on the priesthood presented by Jerome was also important: he opposed the attempts of several deacons who dared to place themselves above the presbyters and affirmed that they could not consecrate the Eucharist, in contradistinction to the bishops and the presbyters Ep. 146. In the treatise De ecclesiastica hierarchia, written by ps.-Dionysius the Areopagite, the bishop is placed at the apex of a holy hierarchy, which is a reflection of the celestial hierarchy; this work, thanks to the supposed apostolic authority of the author, heavily contributed to strengthening the hierarchical conception of the Christian priesthood, at the apex of which was the bishop.
2. Spiritual aspects. From the viewpoint of spiritual theology, this period included the birth of literature on priestly spirituality. In addition to the lost work of Theodore of Mopsuestia’s De sacerdotio, three works of patristic literature have been preserved, which are known by the generic name of the priestly trilogy: Gregory of Nazianzus’s Oratio II, John Chrysostom’s treatise De sacerdotio and Gregory the Great’s Regula pastoralis.
3. Juridical aspects. From the juridical point of view, various aspects must be taken into consideration. 1 Starting from the 4th c., the local church was not restricted to the city but extended to rural areas, with the logical consequence of a new principle of organization that was no longer only urban: the dioceses; this term drew its origin from the political administration of the empire, with the difference that the civil diocese consisted of various provinces. 2 The appointment of the bishops continued to follow the practice of previous centuries: election through the clergy with the approval of the community and ordination by means of a neighboring bishop can. 4 of the Council of Nicaea decreed that the bishops should be ordained by at least three others. An exception to this norm was the appointment of the bishop of Constantinople, an appointment which was subject to the emperor’s authority; moreover, the emperors approved the election of the bishops or they deposed them in the case of the episcopal sees of greater importance.