“Every high priest taken from among men is appointed for men in the things pertaining to God, that he may offer gifts and sacrifices for sins.” (Heb. 5:1)
To understand the priest’s role as mediator between God and man, we must start by making three preliminary points: firstly, that man is social; secondly, that man is a creature; and lastly, that man is sinful.
Situation of mankind
Man is social
What this means is that man, by his very nature, is inclined to establish communities with his fellow men and unite with them in providing for the needs of life and achieving its purpose. Further, since no gathering of people automatically lives together in a state of harmony and productiveness, every group of men needs a leader to unify the whole and direct it.
Man is a creature. At one time he did not exist; at another time he was brought into being. As such, the whole of his being at each moment depends on another, his Creator. Man does not just receive his existence from God, but in fact everything that he has. Because of this state of dependence, man has a duty to render homage to God. This duty is fulfilled by what we call acts of religion.
Putting these first two facts together, we can easily see that men living in society don’t just need presidents and CEOs and heads of families as leaders of various societal units. They also need priests, i.e., men set aside to unite and direct men in the worship rendered by mankind to God. Such is the priest’s defining role, and human societies throughout the ages have set aside certain men to represent them before God, to offer to God on their behalf the choicest gifts of the community.
At this point, we can see already that the priest, by his nature, is a mediator, i.e., one who serves as a link between two parties, God and men. He is an ambassador to the heavenly court, presenting to God the offering of the entire community, paying Him homage, expressing to Him our gratitude, and asking of Him needful favors.
Man is sinful
But there is still one last factor to be taken into account, and this is the fact that man is sinful. The first man, and therefore the natural head of the human race, violated man’s relationship with God by committing a flagrant sin of disobedience. From that point, man did not just need to pay God homage; he also needed to make reparation. In other words, he needed to make atonement for the crime of Adam, primarily, but also for those of the rest of the human race.
This situation is very different from that of innocent man. Before he had offended God, man could offer gifts to God that would be acceptable to Him, though they were not of infinite value. All that was necessary was for man to show his homage to the limit of his capacity as a creature. He need only offer gifts proportionate to his human condition, not ones equal to God’s supreme majesty.
This is not the way that things stand when it comes to making up to God for the crimes committed against Him, for that work is like building a bridge to Heaven, and no mere man can do such a thing. It requires the infinite.
Thus, mankind, after Adam’s sin, found itself in a terrible predicament. God was offended by the human race, and no man could appease Him. The human race was made for God, but now it was impossible to have access to Him. Surely, a greater tragedy cannot be imagined.
Necessity for a Savior
Only God Himself could resolve this situation. And resolve it He did, in the most magnificent and astounding way possible. For He provided the human race with a new head and so a new mediator, who would not just be able to offer gifts equal to God’s majesty, but would also be able to pay an infinite price for the crime of sin. “When the fullness of time was come,” says St. Paul, “God sent his Son, made of a woman... that he might redeem [us]” (Gal. 4:4).
Jesus Christ is both God and man. As God, He is a Divine Person and all of His actions are worthy of God. As man, He is able to represent the interests of the human race before God. Thus, He is not only able to offer some payment for sin, as any man can, but He is able to offer a payment sufficient to reconcile the entire human race. And what is that payment? Himself. Jesus Christ, in His human nature, offers Himself to God on behalf of all mankind, to atone for our infinite crimes, and draw down upon us all manner of divine blessings. This is the Priesthood of Jesus Christ. He is the one Mediator of God and men (1 Tim. 2:5).
What need is there then, one may ask, of merely human priests, after Our Lord’s perfect sacrifice? Well, the fact is that nothing has changed of the three points made above: man is still social, still a creature, and still sinful. Thus, man still needs leaders of religious ceremonies to offer homage and reparation to God on his behalf. There will never be a time here below when men will not have to offer sacrifice to God.
Our Lord Jesus Christ wanted to provide men with the means of re-presenting His own most perfect sacrifice to God, so that its fruits could be applied until the end of time. As such, He gave to certain men the power to act in His name and, by doing so, repeat His perfect mediation with the Father on our behalf. Men receive this power through the sacrament of Holy Orders, and such men are rightly called “other Christs.” This is the nature of the Catholic priesthood: to act in the person of Christ by offering His own sacrifice to God for the payment of sin, as well as the offering of adoration, thanksgiving, and petition.
Let us review and summarize. Because man is social, he does things in groups with his fellow men under the direction of a leader. Because he is a creature, he offers homage to His Creator. Because he is sinful, he must atone for his crimes against God. Jesus Christ the God-man satisfies all three of these most perfectly as a Mediator between God and men. He is the new head of the human race established by God to lead men in their worship of God and to make the perfect reparation necessary to destroy sin.
Catholic priests are given the incredible role and power to act in the person of Jesus Christ. They participate in His priesthood and hence in His mediation. Their highest function is performed at Mass, wherein they offer to God on behalf of all mankind the Body and Blood of Jesus Christ. There is, in fact, no greater thing that a man can do than this: to be the instrument of a perfect mediation between man and God.