Holy orders is a sacrament only taken by some people who wish to devote their whole lives to God and the Church.
The Holy Spirit preserves the continuity of the church through the selection of men who have been set apart for special service to the Catholic church. The bishop lays his hands on these men.
"To the elders among you, I appeal as a fellow elder, a witness of Christ's sufferings and one who also will share in the glory to be revealed. Be shepherds of God's flock that is under your care, serving as overseers- not because you must, but because you are willing, as God wants you to be; not greedy for money, but eager to serve, not lording it over those entrusted to you, but being examples to the flock. And when the Chief Shepherd appears, you will receive the crown of glory that will never fade away."
I Peter 5:1-4