The relations between the Church of this world and the Church of the next are many and various; scarcely less rich and fruitful is the loving and vital fellowship that exists between the earthly members themselves of the Body of Christ. When the Fathers, beginning with Nicetas, bishop of Remesiana at the commencement of the fifth century, speak of the Communion of Saints, they are thinking especially of this earthly fellowship, and it was this that St. Paul also had specially in mind. It is the mysterious inner life of the Church, the mysterious exchange and commerce in functions and graces between its members, the mysterious process whereby the fellowship of Christ grows up organically into a “holy temple in the Lord,” into the habitation of God in the Spirit (Eph. ii, 21-22)

The communion of the members of Christ with the priesthood of their Head is of fundamental importance for their mutual commerce of love. There is but one priesthood in the Church, the priesthood of the God-man, who redeemed us by His whole life, but especially by the sacrifice of His death. But because this invisible priesthood of Christ would make use of visible instruments and organs, so that Christ’s grace may be ministered to His people in sacramental words and signs, there rightly exists in the Church a visible priesthood. And that visible priesthood has existed from the beginning, though its full significance was not at first manifest to the consciousness of the faithful, nor expressed in a precise terminology. Whenever the most holy Eucharist was celebrated and whenever sins were forgiven, whenever the grace of Christ was imparted under visible forms, then instrumental agents were employed, and were called sometimes “presbyteri” or priests, sometimes presidents, sometimes overseers (episcopi). The visible priesthood is nothing else than a visible attestation of the continual living and working of Christ in the world.

However manifold and various its names and duties were and are, there is nevertheless but one single priesthood, since the priesthood of Christ is but one. The priesthood is always only the visible manifestation and mediation of the one grace of the one High Priest. Nevertheless the visible priesthood must have its inner differentiation, according to the intimacy with which its holders are incorporated into the priesthood of Christ, and consequently, according to their sacramental authority to realize that priesthood. It is in this sense that Catholic theology definitely distinguishes the specific priesthood from the priesthood of the laity, and not as though the latter did not imply a genuine participation in the priesthood of Christ. St. Augustine (De civ. Dei, xx, 10) and St. Thomas (Summa, 3, Ixiii, 3) are pre-eminent in insisting that it does. A consideration of the Church’s teaching with regard to the character which is given by some of the sacraments, may make this point clearer.