The sacrament of Holy Orders is conferred in three ranks of clergy: bishops, priests and deacons. Bishops (episcopoi) have the care of multiple congregations and appoint, ordain and discipline priests and deacons. They sometimes appear to be called “evangelists” in the New Testament. Examples of first-century bishops include Timothy and Titus (1 Timothy 5:19-22; 2 Timothy 4:5 and Titus 1:5).
Priests (presbuteroi) are also known as "presbyters" or "elders." In fact, the English term "priest" is simply a contraction of the Greek word presbuteros. They have the responsibility of teaching, governing, and providing the sacraments in a given congregation (1 Tim. 5:17; Jas. 5:14–15).
Deacons (diakonoi) are the assistants of the bishops and are responsible for teaching and administering certain Church tasks, such as the distribution of food (Acts 6:1–6).
In the apostolic age, the terms for these offices were still somewhat fluid. Sometimes a term would be used in a technical sense as the title for an office, sometimes not. This non-technical use of the terms even exists today, as when the term is used in many churches (both Protestant and Catholic) to refer to either ordained ministers (as in “My minister visited him”) or non-ordained individuals. (In a Protestant church one might hear “He is a worship minister,” while in a Catholic church one might hear “He is an extraordinary minister of Holy Communion.”)
Thus, in the apostolic age Paul sometimes described himself as a diakonos ("servant" or "minister"; cf. 2 Cor. 3:6, 6:4, 11:23; Eph. 3:7), even though he held an office much higher than that of a deacon, that of apostle.
Similarly, on one occasion Peter described himself as a "fellow elder," [1 Pet. 5:1] even though he, being an apostle, also had a much higher office than that of an ordinary elder.
The term for bishop, episcopos ("overseer"), was also fluid in meaning. Sometimes it designated the overseer of an individual congregation (the priest), sometimes the person who was the overseer of all the congregations in a city or area (the bishop or evangelist), and sometimes simply the highest-ranking clergyman in the local church—who could be an apostle, if one were staying there at the time.
Although the terms "bishop," "priest," and "deacon" were somewhat fluid in the apostolic age, by the beginning of the second century they had achieved the fixed form in which they are used today to designate the three offices whose functions are clearly distinct in the New Testament.
As the following quotations illustrate, the early Church Fathers recognized all three offices and regarded them as essential to the Church’s structure. Especially significant are the letters of Ignatius, Bishop of Antioch, who traveled from his home city to Rome, where he was executed around A.D. 110. On the way he wrote letters to the churches he passed. Each of these churches possessed the same threefold ministry. Without this threefold ministry, Ignatius said, a group cannot be called a church.
Ignatius of Antioch
"Now, therefore, it has been my privilege to see you in the person of your God-inspired bishop, Damas; and in the persons of your worthy presbyters, Bassus and Apollonius; and my fellow-servant, the deacon, Zotion. What a delight is his company! For he is subject to the bishop as to the grace of God, and to the presbytery as to the law of Jesus Christ" (Letter to the Magnesians 2 [A.D. 110]).
"Take care to do all things in harmony with God, with the bishop presiding in the place of God, and with the presbyters in the place of the council of the apostles, and with the deacons, who are most dear to me, entrusted with the business of Jesus Christ, who was with the Father from the beginning and is at last made manifest" (ibid., 6:1).
"Take care, therefore, to be confirmed in the decrees of the Lord and of the apostles, in order that in everything you do, you may prosper in body and in soul, in faith and in love, in Son and in Father and in Spirit, in beginning and in end, together with your most reverend bishop; and with that fittingly woven spiritual crown, the presbytery; and with the deacons, men of God. Be subject to the bishop and to one another as Jesus Christ was subject to the Father, and the apostles were subject to Christ and to the Father; so that there may be unity in both body and spirit" (ibid., 13:1–2).
"Indeed, when you submit to the bishop as you would to Jesus Christ, it is clear to me that you are living not in the manner of men but as Jesus Christ, who died for us, that through faith in his death you might escape dying. It is necessary, therefore—and such is your practice that you do nothing without the bishop, and that you be subject also to the presbytery, as to the apostles of Jesus Christ our hope, in whom we shall be found, if we live in him. It is necessary also that the deacons, the dispensers of the mysteries [sacraments] of Jesus Christ, be in every way pleasing to all men. For they are not the deacons of food and drink, but servants of the Church of God. They must therefore guard against blame as against fire" (Letter to the Trallians 2:1–3 [A.D. 110]).
"In like manner let everyone respect the deacons as they would respect Jesus Christ, and just as they respect the bishop as a type of the Father, and the presbyters as the council of God and college of the apostles. Without these, it cannot be called a church. I am confident that you accept this, for I have received the exemplar of your love and have it with me in the person of your bishop. His very demeanor is a great lesson and his meekness is his strength. I believe that even the godless do respect him" (ibid., 3:1–2).
"He that is within the sanctuary is pure; but he that is outside the sanctuary is not pure. In other words, anyone who acts without the bishop and the presbytery and the deacons does not have a clear conscience" (ibid., 7:2).
"I cried out while I was in your midst, I spoke with a loud voice, the voice of God: ‘Give heed to the bishop and the presbytery and the deacons.’ Some suspect me of saying this because I had previous knowledge of the division certain persons had caused; but he for whom I am in chains is my witness that I had no knowledge of this from any man. It was the Spirit who kept preaching these words, ‘Do nothing without the bishop, keep your body as the temple of God, love unity, flee from divisions, be imitators of Jesus Christ, as he was imitator of the Father’" (Letter to the Philadelphians 7:1–2 [A.D. 110]).
Clement of Alexandria
"A multitude of other pieces of advice to particular persons is written in the holy books: some for presbyters, some for bishops and deacons; and others for widows, of whom we shall have opportunity to speak elsewhere" (The Instructor of Children 3:12:97:2 [A.D. 191]).
"Even here in the Church the gradations of bishops, presbyters, and deacons happen to be imitations, in my opinion, of the angelic glory and of that arrangement which, the scriptures say, awaits those who have followed in the footsteps of the apostles and who have lived in complete righteousness according to the gospel" (Miscellanies 6:13:107:2 [A.D. 208]).
"When a deacon is to be ordained, he is chosen after the fashion of those things said above, the bishop alone in like manner imposing his hands upon him as we have prescribed. In the ordaining of a deacon, this is the reason why the bishop alone is to impose his hands upon him: he is not ordained to the priesthood, but to serve the bishop and to fulfill the bishop’s command. He has no part in the council of the clergy, but is to attend to his own duties and is to acquaint the bishop with such matters as are needful. . . .
"On a presbyter, however, let the presbyters impose their hands because of the common and like Spirit of the clergy. Even so, the presbyter has only the power to receive [the Spirit], and not the power to give [the Spirit]. That is why a presbyter does not ordain the clergy; for at the ordaining of a presbyter, he but seals while the bishop ordains.
"Over a deacon, then, let the bishop speak thus: ‘O God, who have created all things and have set them in order through your Word; Father of our Lord Jesus Christ, whom you sent to minister to your will and to make clear to us your desires, grant the Holy Spirit of grace and care and diligence to this your servant, whom you have chosen to serve the Church and to offer in your holy places the gifts which are offered to you by your chosen high priests, so that he may serve with a pure heart and without blame, and that, ever giving praise to you, he may be accounted by your good will as worthy of this high office: through your Son Jesus Christ, through whom be glory and honor to you, to the Father and the Son with the Holy Spirit, in your holy Church, both now and through the ages of ages. Amen’" (The Apostolic Tradition 9 [A.D. 215]).
"Not fornication only, but even marriages make us unfit for ecclesiastical honors; for neither a bishop, nor a presbyter, nor a deacon, nor a widow is able to be twice married" (Homilies on Luke17 [A.D. 234]).
Council of Elvira
"Bishops, presbyters, and deacons may not leave their own places for the sake of commerce, nor are they to be traveling about the provinces, frequenting the markets for their own profit. Certainly for the procuring of their own necessities they can send a boy or a freedman or a hireling or a friend or whomever, but, if they wish to engage in business, let them do so within the province" (Canon 18 [A.D. 300]).
Council of Nicaea I
"It has come to the knowledge of the holy and great synod that, in some districts and cities, the deacons administer the Eucharist to the presbyters [i.e., priests], whereas neither canon nor custom permits that they who have no right to offer [the Eucharistic sacrifice] should give the Body of Christ to them that do offer [it]. And this also has been made known, that certain deacons now touch the Eucharist even before the bishops. Let all such practices be utterly done away, and let the deacons remain within their own bounds, knowing that they are the ministers of the bishop and the inferiors of the presbyters. Let them receive the Eucharist according to their order, after the presbyters, and let either the bishop or the presbyter administer to them" (Canon 18 [A.D. 325]).
"[In Philippians 1:1 Paul says,] ‘To the co-bishops and deacons.’ What does this mean? Were there plural bishops of some city? Certainly not! It is the presbyters that [Paul] calls by this title; for these titles were then interchangeable, and the bishop is even called a deacon. That is why, when writing to Timothy, he says, ‘Fulfill your diaconate’ [2 Tim. 4:5], although Timothy was then a bishop. That he was in fact a bishop is clear when Paul says to him, ‘Lay hands on no man lightly’ [1 Tim. 5:22], and again, ‘Which was given you with the laying on of hands of the presbytery’ [1 Tim. 4:14], and presbyters would not have ordained a bishop" (Homilies on Philippians 1:1 [A.D. 402]).
Patrick of Ireland
"I, Patrick, the sinner, am the most rustic and the least of all the faithful . . . had for my father Calpornius, a deacon, a son of Potitus, a priest, who belonged to the village of Bannavem Taberniae. . . . At that time I was barely sixteen years of age . . . and I was led into captivity in Ireland with many thousands of persons, in accordance with our deserts, for we turned away from God, and kept not his commandments, and were not obedient to our priests, who were wont to admonish us for our salvation" (Confession of St. Patrick 1 [A.D. 452]).
"I, Patrick, the sinner, unlearned as everybody knows, avow that I have been established a bishop in Ireland. Most assuredly I believe that I have received from God what I am. And so I dwell in the midst of barbarous heaths, a stranger and an exile for the love of God" (Letter to the Soldiers of Coroticus 1 [A.D. 452]).