10. The Pope is the principle and foundation of unity of the whole Church.
Since the Pope is one only head of the Church with Christ, he is therefore the principle and foundation of unity in the Church. As head of the Church, the Roman Pontiff is the principle of unity of all the faithful. As the head of the body of Bishops, the Roman Pontiff is the principle of unity of the successors to the Apostles, that is, of the Apostolic College. Thus, the Pope unifies all the Shepherds and unifies all the faithful (with the Shepherds of course being also members of the faithful).
* Vatican I, Pastor Aeternus: “In order, then, that the Episcopal office should be one and undivided and that, by the union of the clergy, the whole multitude of believers should be held together in the unity of faith and communion, He set blessed Peter over the rest of the Apostles and instituted in him the permanent principle of both unities and their visible foundation.”
~ Peter and each of his successors are the foundational Rock on which the Church is founded. Then each Roman Pontiff is also the Head of the Church. Therefore, the Church is unified by the Pope as one principle of unity and as one foundation of unity. Christ gave Peter and his successors this role as the permanent principle of both types of unity, from the Head down and from the foundational Rock up. From top to bottom, the Roman Pontiff unifies all the Shepherds and the entire flock.
* Pius XII, Mystical Body of Christ: “But we must not think that He rules only in a hidden or extraordinary manner. On the contrary, our Redeemer also governs His Mystical Body in a visible and normal way through His Vicar on earth. You know, Venerable Brethren, that after He had ruled the ‘little flock’ Himself during His mortal pilgrimage, Christ our Lord, when about to leave this world and return to the Father, entrusted to the Chief of the Apostles the visible government of the entire community He had founded. Since He was all wise He could not leave the body of the Church He had founded as a human society without a visible head. Nor against this may one argue that the primacy of jurisdiction established in the Church gives such a Mystical Body two heads. For Peter in view of his primacy is only Christ’s Vicar; so that there is only one chief Head of this Body, namely Christ, who never ceases Himself to guide the Church invisibly, though at the same time He rules it visibly, through him who is His representative on earth. After His glorious Ascension into Heaven this Church rested not on Him alone, but on Peter, too, its visible foundation stone. That Christ and His Vicar constitute one only Head is the solemn teaching of Our predecessor of immortal memory Boniface VIII in the Apostolic Letter Unam Sanctam; and his successors have never ceased to repeat the same.”
“They, therefore, walk in the path of dangerous error who believe that they can accept Christ as the Head of the Church, while not adhering loyally to His Vicar on earth. They have taken away the visible head, broken the visible bonds of unity and left the Mystical Body of the Redeemer so obscured and so maimed, that those who are seeking the haven of eternal salvation can neither see it nor find it.”
~ The Lord Jesus governs the Church through the Roman Pontiff. Whoever opposes the Roman Pontiff, opposes Christ Jesus. The invisible Head of the Church, Christ, rules the Church through the visible Head, the Roman Pontiff. But Pius XII presents the same teaching as Boniface VIII (Unam Sanctam), that the Church does not have two heads (“like a monster” says Boniface), but only one. This unity between Christ and His Vicar is the clear definitive and longstanding teaching of the Magisterium, and is therefore required belief. Then the same teaching by Boniface is Unam Sanctam was confirmed by the Fifth Lateran Council, making the teaching infallible.
~ Those who wickedly claim that the governing of the Church fell into a “pornocracy” one or more times in the history of the Church are making that nefarious accusation against “Christ, who never ceases Himself to guide the Church invisibly, though at the same time He rules it visibly, through him who is His representative on earth.” Such a gravely sinful claim expresses a definitive rejection of the indefectibility of the Church, as well as a rejection that the Church is truly the Body of Christ, with Christ as Her eternal Head and the Holy Spirit as Her soul. And since the Holy Spirit guides the Church through Her Shepherds, especially the Roman Pontiff, those who accuse the Church of being a “pornocracy” blaspheme against the Holy Spirit. May God judge them.
* Pope Benedict XV, 1914-1922: “1. To Peter the Prince of the Apostles, the divine Founder of the Church allotted the gifts of inerrancy in matters of faith and of union with God. This relationship is similar to that of a ‘Choir Director of the Choir of the Apostles.’ He is the common teacher and rector of all, so that he might feed the flock of Him who established His Church on the authority of Peter himself and his successors. And on this mystical rock the foundation of the entire ecclesiastical structure stands firm as on a hinge. From it rises the unity of Christian charity as well as our Christian faith.”
~ Each Roman Pontiff is the mystical Rock on which the Church is founded. But Christ also is the Rock of the Church: “And they all drank of the same spiritual drink. And so, they all were drinking of the spiritual rock seeking to obtain them; and that rock was Christ.” (1 Cor 10:4). This relation between Christ and His Vicar, such that they are each a Rock for the Church, is like that of the role of Head of the Church. Christ and His Vicar constitute one only Head, and so they also constitute one only Rock of the one Church. And on this mystical Rock, Christ and His Vicar as one Rock, the foundation of the entire Church stands. And this is the only way that the foundation of the Church on Peter and his successors makes sense. As the body of Christ, with Christ as the Head and the Holy Spirit as the soul of the Church cannot be founded solely on fallen sinners who are merely human, as on a Rock, and cannot have only a series of fallen sinners as Head. But when we consider that Christ and the Roman Pontiff are one Head, and Christ and the Roman Pontiff are one Rock, so that from this Rock “rises the unity of Christian charity” and faith, then the teaching fits the nature of the Church as being, like Christ, both human and divine.
* Blessed Pope John Paul I: “From the moment we were elected throughout the days that followed, we were deeply struck and encouraged by the warm manifestations of affection given by our sons and daughters in Rome and also by those sending us from all over the world the expression of their irrepressible jubilation at the fact that God has again given the Church her visible Head. Our mind re-echoes spontaneously the emotion-filled words that our great saintly Predecessor, Saint Leo the Great, addressed to the faithful of Rome: ‘Blessed Peter does not cease to preside over his See. He is bound to the eternal Priest in an unbroken unity … Recognize therefore that all the demonstrations of affection that you have given me because of fraternal amiability or filial devotion have with greater devotedness and truth been given by you and me to him whose See we rejoice to serve rather than preside over it’ (Saint Leo the Great, Sermo V, 4-5: PL 54, 155-156).”
~ Peter still presides over his See. Then Peter and each successive Roman Pontiff is “bound to the eternal Priest in an unbroken unity”. This mystical unity between Christ and His Vicar is what makes the Roman Pontiff the true Head and true Rock of the Church, but only with Christ. However, it can never be truly said that any Pope, due to his own human weaknesses or sins, has failed to be united to Christ, or has failed to be the true Head or true Rock of the Church. For each valid Roman Pontiff has all the papal charisms, including indefectibility.
* Vatican I, Pastor Aeternus: “4. In order, then, that the Episcopal office should be one and undivided and that, by the union of the clergy, the whole multitude of believers should be held together in the unity of faith and communion, He set blessed Peter over the rest of the Apostles and instituted in him the permanent principle of both unities and their visible foundation.”
“2. Therefore we teach and declare that, by divine ordinance, the Roman Church possesses a pre-eminence of ordinary power over every other church, and that this jurisdictional power of the Roman Pontiff is both episcopal and immediate. Both clergy and faithful, of whatever rite and dignity, both singly and collectively, are bound to submit to this power by the duty of hierarchical subordination and true obedience, and this not only in matters concerning faith and morals, but also in those which regard the discipline and government of the Church throughout the world.”
“3. In this way, by unity with the Roman Pontiff in communion and in profession of the same faith, the Church of Christ becomes one flock under one Supreme Shepherd.”
“4. This is the teaching of the Catholic truth, and no one can depart from it without endangering his faith and salvation.”
The First Vatican Council clearly teaches, in unison with the past teachings of the ordinary universal Magisterium, that the Roman Pontiff unifies the body of Bishops by being set over “the rest of the Apostles”. Just as Peter was over the other Apostles, so the successor of Peter is over the successors to the other Apostles. This role as head of the Apostolic College makes the Episcopal office to be “one and undivided”. And then the same principle applies to the body of the faithful (which includes the Bishops). The role of the Roman Pontiff as supreme shepherd of the whole flock, that is, the “whole multitude of believers”, holds them together in the unity of faith and communion.
Notice that it is not enough to have the same faith, the same beliefs; we must also be united in communion. This occurs by submission to the per se authority and role of the Roman Pontiff, not merely by agreement with what he teaches (which soon devolves into judgment of every papal teaching and the multiplication of disagreements). And so we must accept his decision on discipline, including on liturgical matters. This “the duty of hierarchical subordination and true obedience” provides for a unity beyond having the same or similar beliefs, a unity of full communion as one body in Christ.