Choice of the 12 Apostles (the episcops)
And he went up on the mountain, and called to him those whom he desired; and they came to him. And he appointed twelve, to be with him, and to be sent out to preach and have authority to cast out demons: Simon whom he surnamed Peter; James the son of Zebedee and John the brother of James, whom he surnamed Boanerges, that is, sons of thunder; Andrew, and Philip, and Bartholomew, and Matthew, and Thomas, and James the son of Alphaeus, and Thaddaeus, and Simon the Cananaean, and Judas Iscariot, who betrayed him (Mark 3, 13-19).
Choice of the Seventy others (the priests)
After this the Lord appointed seventy others, and sent them on ahead of him, two by two, into every town and place where he himself was about to come. And he said to them, "The harvest is plentiful, but the aborers are few; pray therefore the Lord of the harvest to send out laborers into his harvest [...] (Luke 10, 1-11).
Choice of the Seven (the deacons)
[...] "It is not right that we should give up preaching the word of God to serve tables. Therefore, brethren, pick out from among you seven men of good repute, full of the Spirit and of wisdom, whom we may appoint to this duty. But we will devote ourselves to prayer and to the ministry of the word." And what they said pleased the whole multitude, and they chose Stephen, a man full of faith and of the Holy Spirit, and Philip, and Prochorus, and Nicanor, and Timon, and Parmenas, and Nicolaus, a proselyte of Antioch. These they set before the apostles, and they prayed and laid their hands upon them (Acts 6, 1-6).
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The sacrament of Holy Orders is the sacrament through which the mission entrusted by Christ to his apostles continues to be exercised in the Church until the end of time.
Orders designates an ecclesial body into which one enters by means of a special consecration (ordination). Through a special gift of the Holy Spirit, this sacrament enables the ordained to exercise a sacred power in the name and with the authority of Christ for the service of the People of God.
The sacrament of Holy Orders is composed of three degrees which are irreplaceable for the organic structure of the Church: the episcopate, the presbyterate and the diaconate.
Episcopal ordination confers the fullness of the sacrament of Holy Orders. It makes the bishop a legitimate successor of the apostles and integrates him into the episcopal college to share with the Pope and the other bishops care for all the churches. It confers on him the offices of teaching, sanctifying, and ruling.
The bishop to whom the care of a particular Church is entrusted is the visible head and foundation of unity for that Church. For the sake of that Church, as vicar of Christ, he fulfills the office of shepherd and is assisted by his own priests and deacons.
The anointing of the Spirit seals the priest with an indelible, spiritual character that configures him to Christ the priest and enables him to act in the name of Christ the Head. As a co-worker of the order of bishops he is consecrated to preach the Gospel, to celebrate divine worship, especially the Eucharist from which his ministry draws its strength, and to be a shepherd of the faithful.
The deacon, configured to Christ the servant of all, is ordained for service to the Church. (CCC).
