Jesus Christ is the High Priest because He serves as the Bridge, the Mediator, between man and God, and because He offered His one-for-all atoning sacrifice on Calvary, which was infinitely sufficient, for the salvation of all mankind. However, He also willed to ordain priests (men ordained in His line of priesthood) who would act in His Person on earth, and through whom He would work in a special way – forgiving sins, etc.
What distinguishes a priest from everyone else is his ability to celebrate the sacraments; and the highest and most sublime act of the priest is to offer the Most Holy Sacrifice of the Mass, for by Holy Mass, Christ is made really, truly, and substantially present amongst us.
A priest does not become a priest because he completes the required number of years in the seminary or because he has reached a certain degree of intellectual prowess, but because he receives the grace of the Sacrament of Holy Orders, which Christ instituted at the Last Supper when He said to His apostles after He had instituted the Most Holy Eucharist: “Do this in remembrance of me” (Lk 22:19). Thus the priest ought to become a total offering to God. His whole life ought to imitate the Holy Mass, being one continual sacrifice for the salvation of the world, which he continues until his death, just as Christ continued until His death. Laity ought to also to imitate this example of total self-giving to God and to others for God’s sake, and so to persevere in God’s will until their deaths.
Bound with the priesthood of Jesus Christ is the understanding of apostolic succession. Every bishop can trace their lineage (of ordination) back to one of the apostles. Hence, all bishops, who form the ordinary magisterium of the Church, have apostolic authority to teach, and possess the “fullness” of the sacrament of Holy Orders, enabling them to celebrate all of the Church’s seven sacraments.
The matter of the Sacrament of Holy Orders is the bishop’s laying on of hands on the baptized male’s head. The form is a prayer of ordination prayed by the bishop over the man. The minister is a bishop and only a bishop because only he possesses the fullness of apostolic authority.
Deacons also receive the Sacrament of Holy Orders, though they can only celebrate the Sacraments of Baptism and Marriage. They can assist in a special way at Holy Mass and can minister the Most Holy Eucharist. They have also traditionally worked especially for the welfare of the poor and the social buildup of the Church.
In the Latin Rite (Western Church), a priest must celibate and thus of course cannot be married. A permanent deacon (priests are ordained as transitional deacons before they are ordained priests) can be married, but must be married before he becomes a permanent deacon and can only become a permanent deacon once he has reached the age of 35. In the Eastern Rites of the Church, a priest can be married, but only after if he marries before he is ordained. A bishop, however, cannot be married. The differences in this liturgical practice has developed over time and does not affect in any way the sacrament’s integrity. There is theological reason for both rites’ practices. While both practices are matters of discipline, not of objective truths of faith or morals, they are so set in stone in each tradition, that they are likely never to change.
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Why can’t women be priests?
Women cannot be priests because God does not will them to be priests. The priest acts in a special way in Persona Christi, above all at the Most Holy Sacrifice of the Mass, wherein He speaks as Christ when He utters the words of institution of the Holy Eucharist. On a practical level, the priest should be conformed to Christ as closely as possible, of course in charity as everyone ought to be, but even in his biological sex.
Moreover, Christ instituted the priesthood at the Last Supper, as discussed above, He instituted it to His twelve apostles, all of whom were male. He was revolutionary in His inclusion of women in His ministry – He exalted the Blessed Virgin Mary above all angels and saints without exception, He drove seven demons out of St. Mary Magdalene, interacted with the woman at the well, admired the Syrophoenician woman’s faith, and allowed women to be among some of His most intimate followers. Yet He did not ordain any of them to the priesthood. Therefore, Christ’s decision to exclude women from the priesthood should not be understood as a denigration of women – it is not; nor should it be understood as an exaltation of men above women, for Judas Iscariot was among the first priests. Rather, it is received as an Article of Faith that only men may be ordained to the priesthood, not because of any merit of theirs, but because of God’s grace and His will.