In his letter to Timothy, St. Paul reminds his disciple to "rekindle the gift of God that is within you through the laying on of hands." It is through that action, the laying on of hands, that the graces of the priesthood have been handed on from age to age. In the Catholic Church, all deacons, priests and bishops can directly trace the validity of their ordination to the Apostles (apostolic succession).
As we read in the Catechism of the Catholic Church (1578), "No one as a right to receive the sacrament of Holy Orders. Indeed no one claims this office for himself; he is called to it by God. Anyone who thinks he recognizes the signs of God's call to the ordained ministry must humbly submit his desire to the authority of the Church, who has the responsibility and the right to call someone to receive orders. Like every grace, this sacrament can be received only as an unmerited gift."
The duly ordained priest stands in persona Christi - or in the person of Christ - especially in dispensing the sacraments. He takes vows of celibacy and obedience, offering his whole life for the life of the Church.