ABOVE: Marianists Brandon Paluch and Michael Chiuri at their ordination.
THE WHAT AND THE WHY
St. Paul tells us that the Holy Spirit gives many gifts, and distributes them as He chooses. He cites the gifts of prophecy, of teaching, of healing, of administration, etc., and tells us that such gifts are given not for the person himself or herself but for the building up of the Church, which Christ considers His own spiritual body.
Jesus himself set up Peter as the rock on which He would build His church, and gave him, figuratively, the keys to the Kingdom. The keys represent authority. Peter became the Vicar of Christ, his delegate on earth, and the other Apostles became, in union with him, the governing body of the Church.
Jesus gave them tremendous responsibility. Yes, for managing the affairs of the Church, but also for the vitality of the Church. They were the first teachers, and they remain the chosen teachers of Christ's people. As the Church grew, it became necessary to organize in more detail, so deacons were appointed to certain works of the Church. Not long after that came the presbyters, now called priests. The successors of the Apostles came to be called bishops. All of these men were recognized as set aside and delegated; the Sacrament of Orders becoming the means of doing this. By it, men are ordained to take responsibility for the spiritual health and well-being of all believers.
Jesus is described as having several roles besides Savior, including king, prophet, priest and teacher. All baptized believers share in some way in these roles, but the ordained men do so more specifically and carry a heavier responsibility.
We call most of the ordained men priests. (Some are deacons.) In the Old Testament, the main role of priests was to offer the Temple sacrifices on behalf of the people. In the New Testament -- our times -- they do the same when they celebrate Mass. The Mass is, among other things, the way in which Jesus offers His sacrifice, the one He offered from the Cross, to the Father in our times and in our communities, so that we can join with Him in offering it. The priest is the one designated to do this; it is the meaning of his priesthood. In addition, he is responsible for making the sacraments available to the faithful, and along with the bishops, for protecting the truth of the Gospel among believers.
Ordination can be received only once, and it is for life. A candidate for priesthood must be prepared to make such a serious commitment.
Others who are not priests also make lifelong commitments. Married persons are the most numerous. But there are also the "eunuchs for the kingdom of heaven": women who are called Religious Sisters or nuns, and men who are called Religious Brothers. These are dedicated to prayer and community and service as a way of life, but are not delegated the same kind of responsibility as priests have. They do not receive Holy Orders.
Men who feel called by God to become diocesan priests must apply to the diocese and be accepted for ordination by a bishop. People thinking about joining a Religious Community must apply to that Religious Order.