Jesus chose 12 men to be apostles. One of them, Judas, betrayed Jesus, and then hanged himself. After Jesus' ascension, the apostles had the important mission of spreading the news about Jesus, but they were lacking one member. At a gathering of Jesus' disciples, Peter told the group that a replacement for Judas was needed. The man to be chosen needed to have been a witness to Jesus' life, death, resurrection, and ascension. Two men were proposed, Justus and Matthias. Peter and the apostles prayed for the Lord to show them whom to choose. Matthias was chosen and became the new apostle (Acts 1:15-26).
The apostles chose a new Church leader to be a witness to Jesus Christ and continue his work. Today the pope and bishops have been called and chosen to continue Jesus' work; they are successors to the apostles.
All members of the Church participate in the priesthood of all believers through Baptism. However, some men are called to serve Jesus and the Church today through the celebration of the Sacrament of Holy Orders. Through their leadership in the Church, they help continue Jesus' presence on earth in the tradition of the apostles.
Those who are called to be priests are ordained through the Rite of Ordination. In celebrating this Rite, men receive a permanent spiritual mark, called a character, signifying that they represent Jesus' presence in the Church.
There are three levels of participation in the Sacrament of Holy Orders: as bishop, as priest (from presbyter, which is Greek for “elder”), and as deacon.
A bishop receives the fullness of the Sacrament of Holy Orders. He is the head or Ordinary of the local church. The local area entrusted to him is called a diocese. A bishop is also a member of the episcopal college: this is all the bishops who, with the pope, guide the Church.
Priests serve the community in various ways. They may be called to serve in their dioceses or as religious order priests, carrying out the mission of a particular religious community. They preside at liturgies, preach, administer the sacraments, counsel people, serve as pastors, and teach.
Deacons help and serve bishops by serving the needs of the Church, proclaiming the gospel, teaching and preaching, baptizing, witnessing marriages, and assisting the priest celebrant at liturgies.
Deacons are ordained for service in the Church. There are deacons who are studying to become priests. There are deacons that include married men who are called to remain deacons for life and to serve the Church in this capacity.
Priests receive the Sacrament of Holy Orders in the Rite of Ordination. The bishop lays his hands on the head of the candidate and says a prayer asking for the outpouring of the Holy Spirit. In one part of the rite, the candidate lies in front of the altar while the Litany of the Saints is sung or recited. In another part of the rite, a priest's hands are anointed with chrism. In the rite for a bishop, the new bishop's head is anointed.