Acts 13:2-3
While they were worshiping the Lord and fasting, the Holy Spirit said, "Set apart for me Barnabas and Saul for the work to which I have called them." Then after fasting and praying they laid their hands on them and sent them off.
The essential core of the Sacrament of Holy Orders is, according to the Catechism of the Catholic Church, "the bishop's imposition of hands on the head of the ordinand and in the bishop's specific consecratory prayer asking God for the outpouring of the Holy Spirit and his gifts proper to the ministry to which the candidate is being ordained". There is something warm and human about this, and it is significant that the essence of this tradition is a gesture as much as a word. We live in a culture that values abstraction more than reality and that sees statistics as somehow more real than the living breathing people they represent. In a perfect counter-cultural, er, gesture the Church see to the handing down of apostolic authority, not merely through an abstraction or a by means of passing a theology quiz, but by the imposition of warm human hands, palm to pate, down through the ages. This is in keeping with the central core of the Christian faith itself, which insists that God's ultimate revelation is not the Word made Abstraction, but the Word made flesh. That is why the way in which Paul and Barnabas were ordained is still the way bishops, priests, and deacons are ordained today. God still manifests his power through the hands of human beings and bestows the Holy Spirit on his priests for our good.
