The bishop-elect did not necessarily have to belong to the city’s clergy, but he had to be known to them; even laymen could be elected, but from the 4th c. legislation favored a choice from among the clergy according to the Council of Serdica can. 10, which prescribed that he must be a lector, deacon or presbyter; Leo the Great also required a cursus, as a guarantee of his preparation. Meanwhile the practice of ordaining hermits or monks a category not then belonging to the clergy increased, in the hope that they had more preparation and, particularly, that they practiced continence. Monks aspired to the priesthood, seeing it as a means of social advancement.
It was the bishop who chose all the other members of the clergy, though he took advice from others, esp. the presbyters: When it comes to ordaining clerics, we are accustomed to consulting you before their ordination and examining each one’s morals and merits in a public assembly Cypr., Ep 38, 1; cf. Orig., In Matth. 16, 21-22; Didasc. apost. 2, 34. The people also intervened in the nomination of presbyters, but probably not always. At times presbyters were ordained by urgent popular demand, as with Cyprian, Ambrose, Paulinus of Nola, Augustine, Jerome’s brother Paulinianus and Nepotianus. The growing difficulty of recruiting people specifically prepared for the ministry led to the idea of preparing future cadres, as suggested by Pope Siricius Ep. 1,9: PL 13, 1142-1143 and done by some great spirits, e.g., Eusebius of Vercelli and Augustine. The Pastoral Epistles give indications, esp. moral ones, for the choice of a good bishop or a deacon 1 Tim 3:2-13; Tit 1:6. A neophyte or a twice-married man could not be a bishop 1 Tim 3:2, 6 and, by the 3rd c., those who had done public penitence or had been voluntarily mutilated or baptized during a grave illness clinici were ordinarily not admitted, not just to the episcopate, but to the clergy. We know some cases of neophytes who, by popular demand, were ordained bishops: Ambrose, Synesius of Cyrene, Nectarius of Constantinople. Interdictions, both civil and ecclesiastical, on admission to the clergy became numerous in the 4th c. and greatly limited choice.
Professions unacceptable to the church included those involved in entertainment, state officials, soldiers baptized before military service, administrators of others’ goods until they had finally accounted for their charge, and slaves and freedmen because they did not enjoy full civil liberty. The state too, for economic reasons, banned certain categories of people from entering the clergy: slaves and coloni without the written permission of their patronus, butchers and bakers, junior officials of various public services, employees of imperial industries, curiales, etc., those who possessed sufficient wealth: It is right that the rich should assist the needs of the time and the poor should be sustained by the wealth of the church CTh 16,2,6; cf. 16,2,3. It was permitted to clarissimi, senators but these were few and it was not always convenient for them and to those in liberal professions lawyers, professors who because of their activities were not always acceptable to the church.