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 Tim. 5:19–22; 2 Tim. 4:5; 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 first centuries] the term for bishop, episcopos ("overseer"), was 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]).