Encyclical of Pope Leo XIII On the Unity of the Church
Abridged from sections 10 through 15.
Indeed no true and perfect human society can be conceived which is not governed by some supreme authority. Christ therefore must have given to His Church a supreme authority to which all Christians must render obedience. For this reason, as the unity of the faith is of necessity required for the unity of the church, inasmuch as it is the body of the faithful, so also for this same unity, inasmuch as the Church is a divinely constituted society, unity of government, which effects and involves unity of communion, is necessary jure divino [by divine law].
The nature of this supreme authority, which all Christians are bound to obey, can be ascertained only by finding out what was the evident and positive will of Christ. Certainly Christ is a King for ever; and though invisible, He continues unto the end of time to govern and guard His church from Heaven. But since He willed that His kingdom should be visible He was obliged, when He ascended into Heaven, to designate a vice-regent on earth. "Therefore, because He was about to withdraw His visible presence from the Church, it was necessary that He should appoint someone in His place, to have the charge of the Universal Church. Hence before His Ascension He said to Peter: 'Feed my sheep'" (St. Thomas, Contra Gentiles, lib. iv., cap. 76).
Jesus Christ, therefore, appointed Peter to be that head of the Church; and He also determined that the authority instituted in perpetuity for the salvation of all should be inherited by His successors, in whom the same permanent authority of Peter himself should continue. And so He made that remarkable promise to Peter and to no one else: "Thou are Peter, and upon this rock I will build my church" (Matt. xvi., 18).
From this text it is clear that by the will and command of God the Church rests upon St. Peter, just as a building rests on its foundation. Now the proper nature of a foundation is to be a principle of cohesion for the various parts of the building. It must be the necessary condition of stability and strength. Remove it and the whole building falls. It is consequently the office of St. Peter to support the Church, and to guard it in all its strength and indestructible unity. How could he fulfil this office without the power of commanding, forbidding, and judging, which is properly called jurisdiction? It is only by this power of jurisdiction that nations and commonwealths are held together. God confided His Church to Peter so that he might safely guard it with his unconquerable power. He invested him, therefore, with the needful authority; since the right to rule is absolutely required by him who has to guard human society really and effectively. This, furthermore, Christ gave: "To thee will I give the keys of the kingdom of Heaven." The Church is typified not only as an edifice but as a Kingdom, and every one knows that the keys constitute the usual sign of governing authority. Wherefore when Christ promised to give to Peter the keys of the Kingdom of Heaven, he promised to give him power and authority over the Church.
The promise is carried out when Christ the Lord after His Resurrection, having thrice asked Peter whether he loved Him more than the rest, lays on him the injunction: "Feed my lambs - feed my sheep."
It was necessary that a government of this kind, since it belongs to the constitution and formation of the Church, as its principal element - that is as the principle of unity and the foundation of lasting stability - should in no wise come to an end with St. Peter, but should pass to his successors from one to another. For this reason the Pontiffs who succeed Peter in the Roman Episcopate receive the supreme power in the church, jure divino.
Who is unaware of the many and evident testimonies of the holy Fathers which exist to this effect? Most remarkable is that of St. Irenaeus who, referring to the Roman Church, says: "With this Church, on account of its preeminent authority, it is necessary that every Church should be in concord" (Contra Haereses, lib. iii., cap. 3, n. 2). For this reason Jerome addresses Damasus thus: "My words are spoken to the successor of the Fisherman, to the disciple of the Cross.... I communicate with none save your Blessedness, that is with the chair of Peter. For this I know is the rock on which the Church is built" (Ep. xv., ad Damasum, n. 2). And for a like reason St. Augustine publicly attests that, "the primacy of the Apostolic chair always existed in the Roman Church" (Ep. xliii., n. 7); and he denies that anyone who dissents from the Roman faith can be a Catholic. "You are not to be looked upon as holding the true Catholic faith if you do not teach that the faith of Rome is to be held" (Sermo cxx., n. 13). In the same way Maximus the Abbot teaches that obedience to the Roman Pontiff is the proof of the true faith and of legitimate communion. "Therefore if a man does not want to be, or to be called, a heretic, let him not strive to please this or that man...but let him hasten before all things to be in communion with the Roman See" (Defloratio ex Epistola ad Petrum illustrem).
But if the authority of Peter and his successors is plenary and supreme, it is not to be regarded as the sole authority. For He who made Peter the foundation of the Church also "chose, twelve, whom He called apostles" (Luke vi., 13); and just as it is necessary that the authority of Peter should be perpetuated in the Roman Pontiff, so, by the fact that the bishops succeed the Apostles, they inherit their ordinary power, and thus the episcopal order necessarily belongs to the essential constitution of the Church. Although they do not receive plenary, or universal, or supreme authority, they are not to be looked as vicars of the Roman Pontiffs; because they exercise a power really their own, and are most truly called the ordinary pastors of the peoples over whom they rule.
But since the successor of Peter is one, and those of the Apostles are many, it is necessary to examine into the relations which exist between him and them according to the divine constitution of the Church. Above all things the need of union between the bishops and the successors of Peter is clear and undeniable. This bond once broken, Christians would be separated and scattered, and would in no wise form one body and one flock.
From this it must be clearly understood that Bishops are deprived of the right and power of ruling, if they deliberately secede from Peter and his successors; because, by this secession, they are separated from the foundation on which the whole edifice must rest. They are therefore outside the edifice itself; and for this very reason they are separated from the fold, whose leader is the Chief Pastor; they are exiled from the Kingdom, the keys of which were given by Christ to Peter alone.
But the Episcopal order is rightly judged to be in communion with Peter, as Christ commanded, if it be subject to and obeys Peter; otherwise it necessarily becomes a lawless and disorderly crowd. It is not sufficient for the due preservation of the unity of the faith that the head should merely have been charged with the office of superintendent, or should have been invested solely with a power of direction. But it is absolutely necessary that he should have received real and sovereign authority which the whole community is bound to obey.
But it is opposed to the truth, and in evident contradiction with the divine constitution of the Church, to hold that while each Bishop is individually bound to obey the authority of the Roman Pontiffs, taken collectively the Bishops are not so bound.
So the Roman Pontiffs, mindful of their duty, wish above all things, that the divine constitution of the Church should be preserved. Therefore, as they defend with all necessary care and vigilance their own authority, so they have always laboured, and will continue to labour, that the authority of the bishops may be upheld.
[Satis cognitum, in its unabridged form, contains many more texts from the Fathers of the Church in support of each of its points.]
Abridged from Leo XIII's encylical letter Satis cognitum, "On the Unity of the Church,"29 June 1896.