The Foundation of Unity

One Body, One Head

Therefore, of the one and only Church (there is) one body, one head, not two heads as a monster, namely, Christ and Peter, the Vicar of Christ and the successor of Peter, the Lord Himself saying to Peter: “Feed my sheep” (Jn 21:17). He said “my,” and generally, not individually these or those, through which it is understood that He entrusted all to him. […]

But this authority, although it is given to man and is exercised by man, is not human, but rather divine, and has been given by the divine Word to Peter himself and to his successors in him, whom the Lord acknowledged an established rock.

Excerpts from: BONIFACE VIII. Unam sanctam,
18/11/1302: DH 872; 874

Peter, Visible Foundation of Unity

The eternal Pastor and Bishop of our souls, in order to render the saving work of Redemption perennial, willed to build a holy Church, in which, as in the house of the living God, all the faithful might be contained by the bond of one faith and charity. […]

But, that the episcopacy itself might be one and undivided, and that the entire multitude of the faithful through priests closely connected with one another might be preserved in the unity of faith and communion, placing the blessed Peter over the other apostles He established in him the perpetual principle and visible foundation of both unities.

Excerpts from: PIUS IX.
Pastor æternus, Constitution of the First Vatican Council,
18/7/1870: DH 3050-3051

Role to Guard the Unity of the Church

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.

Excerpt from: LEO XIII.
Satis cognitum, 29/6/1896

Bearing Witness to the Truth, He Serves Unity

With the power and the authority without which such an office would be illusory, the Bishop of Rome must ensure the communion of all the Churches. For this reason, he is the first servant of unity. This primacy is exercised on various levels, including vigilance over the handing down of the Word, liturgical and sacramental celebration, and the Church’s mission, discipline and the Christian life.

It is the responsibility of the Successor of Peter to recall the requirements of the common good of the Church, should anyone be tempted to overlook it in the pursuit of personal interests. He has the duty to admonish, to caution and at times to declare that this or that opinion being circulated is irreconcilable with the unity of the Faith. When circumstances require it, he speaks in the name of all the Pastors in communion with him. He can also – under very specific conditions clearly laid down by the First Vatican Council – declare ex cathedra that a certain doctrine belongs to the deposit of the Faith. By thus bearing witness to the truth, he serves unity.

Excerpt from: ST. JOHN PAUL II.
Ut unum sint, 25/5/1995

Guarding the Deposit of the Faith, Guarantee of Church Unity

The Holy Spirit was not promised to the successors of Peter that by His revelation they might disclose new doctrine, but that by His help they might guard sacredly the revelation transmitted through the Apostles and the deposit of the Faith, and might faithfully set it forth. […]

So, this gift of truth and a never failing faith was divinely conferred upon Peter and his successors in this chair, that they might administer their high duty for the salvation of all; that the entire flock of Christ, turned away by them from the poisonous food of error, might be nourished on the sustenance of heavenly doctrine, that with the occasion of schism removed the whole Church might be saved as one.

Excerpts from: PIUS IX.
Pastor æternus, Constitution of the First Vatican Council,
18/7/1870: DH 3070-3071

Mission to Reaffirm What the Church Received from the Beginning

The mission of Peter and his successors consists in establishing and authoritatively reaffirming what the Church received and believed from the beginning, what the Apostles taught, what Sacred Scripture and Christian Tradition established as the object of faith and the Christian norm of life. […] The content of the teaching of the successor of Peter […], in its essence, is a witness to Christ, to the event of the Incarnation and the Redemption, as well as to the presence and action of the Holy Spirit in the Church and in history.

Excerpts from: ST. JOHN PAUL II.
General Audience, 10/3/1993

Strengthen the Faith amidst the World’s Contradictions

Jesus prays in a particular way for Peter: “…that your faith may not fail” (Lk 22:32a). Jesus’ prayer is at the same time a promise and a duty. Jesus’ prayer safeguards Peter’s faith, that faith which he confessed at Caesarea Philippi: “You are the Christ, the Son of the living God” (Mt 16: 16).

And so, never let this faith be silenced; strengthen it ever anew, even in the face of the cross and all the world’s contradictions: this is Peter’s task. Therefore, the Lord prays not only for Peter’s personal faith, but for his faith as a service to others. This is exactly what He means with the words: “When you have turned again, strengthen your brethren” (Lk 22:32b).

Excerpt from: BENEDICT XVI.
Homily, 29/6/2006

Divine Disposition, Beyond the Scope of Human Arbitrariness

[The Pope] is under divine law and bound to the provisions established by Christ for His Church. He cannot modify the constitution given to the Church by her Divine Founder in the way that a temporal legislator can modify the constitution of the State. The constitution of the Church is founded, in all its essential points, on a divine disposition beyond the scope of human arbitrariness.

Excerpt from: PIUS IX.
Replies to the circular of Chancellor Bismarck,
January-March of 1875: DH 3114

A Man Called to Participate in Divine Power

When [Peter] had said, “You are Christ, the Son of the living God,” Jesus answered, “Blessed are you, Simon son of Jonah, for it was not a human being who revealed this to you, but my Father in Heaven” (Mt 16:16-17). […] “Therefore I say to you,” He added, as the Father has revealed my divinity to you, I also reveal your dignity to you: “You are Peter” (Mt 16:18). This means that I am the unbreakable rock, the chief stone that out of two peoples I make one (cf. Eph 2:20, 14), the foundation upon which no one can lay another. However, you are also a rock, because you share my strength. In this way, the power that is mine by personal prerogative will be given to you through your participation with Me.

Excerpts from: ST. LEO THE GREAT.
Sermo IV, c.2: PL 54, 149-150