The teaching of the ordinary universal magisterium, confirmed infallibly by the First Vatican Council, is that Peter and his successors each have the charism of truth and never-failing faith. And since apostasy, heresy, schism, idolatry, and blasphemy are each and all a grave failing of faith, the Roman Pontiff can never fall into any of these sins. (Now in the article, I will focus on heresy, but the same applies to all the other grave failings of faith.)

This charism of truth and never-failing faith, by means of prevenient grace which no one can resist, preserves every valid Roman Pontiff from teaching material heresy, as heresy is always contrary to the truths of the faith, and from committing formal heresy, whether publicly or privately or even merely interiorly, as heretics by definition have gravely failed in faith. And this grace of truth and never-failing faith certainly affects the Roman Pontiff first and foremost interiorly, in his heart and mind and soul, as well as in his exterior acts, since exterior acts always spring from the interior of the person.

My comments on the quotes below are preceded by a tilda ~

Vatican I:
“So the fathers of the fourth Council of Constantinople, following the footsteps of their predecessors, published this solemn profession of faith: ‘The first condition of salvation is to maintain the rule of the true faith. And since that saying of our Lord Jesus Christ, “You are Peter, and upon this rock I will build my Church,” cannot fail of its effect, the words spoken are confirmed by their consequences. For in the Apostolic See the Catholic religion has always been preserved unblemished, and sacred doctrine been held in honor.’ ”

~ Peter and each of his successors is a rock of faith, and the See of the Roman Pontiff has always been preserved by the grace of God unblemished. But if material heresy were taught by the Pope, this would be a blemish on the See. And if a Pope were to fail in faith by heresy (or in any other way), then he would not be a rock on which the Church could be founded. For if the foundation of a house built upon a rock fails, that house would fall [Mt 7:24-29], which is impossible for the Church due to the indefectibility promised by Christ in Mt 16:18 and due to the fact that the Church is the body of Christ with Christ as Her eternal head.

Vatican I: “It was for this reason that the bishops of the whole world, sometimes individually, sometimes gathered in synods, according to the long established custom of the Churches and the pattern of ancient usage referred to this Apostolic See those dangers especially which arose in matters concerning the faith. This was to ensure that any damage suffered by the faith should be repaired in that place above all where the faith can know no failing.”

~ The ancient constant practice of the Church is to refer matters that might endanger the faith to the Apostolic See, since that is the “place above all where the faith can know no failing”. This is due to the charism of truth and never-failing faith, as Vatican I teaches later in the same document.

Vatican I: “Indeed, their apostolic teaching was embraced by all the venerable fathers and reverenced and followed by all the holy orthodox doctors, for they knew very well that this See of St. Peter always remains unblemished by any error, in accordance with the divine promise of our Lord and Savior to the prince of his disciples: ‘I have prayed for you that your faith may not fail; and when you have turned again, strengthen your brethren [Lk 22:32].’

“This gift [Latin: charisma] of truth and never-failing faith was therefore divinely conferred on Peter and his successors in this See so that they might discharge their exalted office for the salvation of all, and so that the whole flock of Christ might be kept away by them from the poisonous food of error and be nourished with the sustenance of heavenly doctrine. Thus the tendency to schism is removed and the whole Church is preserved in unity, and, resting on its foundation, can stand firm against the gates of hell [Mt 16:18].”

~ The First Vatican Council teaches that Peter and each of his successors has the gift or charism of truth and never-failing faith. The purpose of this gift is to contribute to the salvation offered by the Church, to keep the faithful from grave error, and to nourish their souls with true doctrine. The effect of this charism is to secure the indefectibility of the Church. For the reference to the Church standing “firm against the gates of Hell” is from Mt 16:18, the verse that is the basis for the dogma of the indefectibility of the Church.

Vatican I: “What is more, with the approval of the second Council of Lyons, the Greeks made the following profession: ‘The Holy Roman Church possesses the supreme and full primacy and principality over the whole Catholic Church. She truly and humbly acknowledges that she received this from the Lord himself in blessed Peter, the prince and chief of the apostles, whose successor the Roman Pontiff is, together with the fullness of power. And since before all others she has the duty of defending the truth of the faith, so if any questions arise concerning the faith, it is by her judgment that they must be settled.’ ”

~ The supreme authority of the Roman Pontiff is protected from misuse by the charism of truth and never-failing faith. Therefore, due to both the Pope’s supreme authority and his never-failing faith, all questions concerning the Faith “must be settled” by “her judgment”, meaning by the judgment of the Roman See of the successor of Peter. Those who reject this authority are schismatics. Those who claim that the question of faith settled by the Roman Pontiff errs to the extent of heresy are themselves heretics. For this teaching of the never-failing faith of the Roman Pontiff is established as infallible by the ordinary universal magisterium and by the First Vatican Council.

Teachings from the ordinary universal magisterium:
See the full set of quotes with all references here.

Saint Irenaeus, Doctor, 130-202: “But, since it would be very long to count up the succession of all Churches in such a book as this, by showing the tradition of the greatest and oldest Church, known to all, founded and established by the two most glorious apostles, Peter and Paul, at Rome, which [tradition] She has from the apostles, and by showing the faith proclaimed to men through the series of her bishops down to us, we confound all who, in any way, gather beyond what is right, either to please themselves, or for vainglory, or by blindness and wrong opinion. For to this Church, because of Her mightier rule, every Church must agree, that is, those who are faithful from all sides, in which the tradition from the apostles is kept by those who are from all sides.”

Origen, 184-253: “It is manifest, even if it were not expressed, because the gates of Hell can prevail against neither Peter, nor the Church, for if they prevailed against the rock on which the Church was founded, they would prevail against the Church.” [Mt 16:18]

Origen, 184-253: “neither against the rock upon which Christ builds His Church, nor against the Church, shall the gates of Hell prevail.”

Saint Cyprian, Bishop, 210-258: “Where Peter is, there is the Church”, repeated by Saint Ambrose and Saint Boniface. Confirmed by Pope Benedict XV, in the encyclical In Hac Tanta.

Saint Cyprian: “If someone does not hold fast to this unity of Peter, can he imagine that he still holds the faith? If he desert the chair of Peter upon whom the Church was built, can he still be confident that he is in the Church?”

Saint Cyprian: “The Church which is Catholic and one is not broken nor divided; it is united and joined by the cement of bishops who agree together.”

~ The true Pope is that Bishop of Rome who is followed by the Bishops as a body. For neither the Roman Pontiff as an individual, nor the bishops as a body, can go astray or lead astray, lest the Church fail to be one, holy, apostolic and catholic, and thereby lose Her indefectibility (which is impossible).

Pope Saint Lucius I, Martyr, 253-254: “The Roman Apostolic Church is the mother of all Churches and has never been shown to have wandered from the path of Apostolic tradition, nor being deformed, succumbed to heretical novelties according to the promise of the Lord himself, saying, ‘I have prayed for thee, etc.’ [Lk 22:32]”

~ Here is one of many teachings explicitly stating that the Roman Pontiff and the Apostolic See led by him can never fall into heresy. There are many different wordings, but the same teaching, that the Roman Pontiff cannot fail in faith, cannot succumb to heresy, cannot wander from the path of Apostolic tradition, etc. These many different wordings, all teaching the same doctrine, proves that this charism of truth and never-failing faith is the ancient constant teaching of the Church, finally confirmed by Vatican I, and is therefore an infallible teaching of the ordinary universal magisterium.

Pope Saint Felix I, 269-274, speaking on the Roman Church: “As it took up in the beginning the norm of the Christian Faith from its authors, the Princes of the Apostles of Christ, She remains unsullied according to what the Lord said: ‘I have prayed for thee, etc.’ [Lk 22:32]”

~ The “Princes of the Apostles” are the successive Roman Pontiffs. The Roman Church is “unsullied” by any grave error or heresy. And this is the constant interpretation of Luke 22:32 by the Popes, Saints, Fathers, Doctors, and Councils.

Theodotus of Ancyra, martyr, fl. 303: “This holy See holds the reign of the Churches of the world, not only on account of other things, but also because She remains free from the heretical stench.”

Saint Ephrem the Syrian, Doctor, 306-373: “The heavenly spouse has established the Church and made her firm in the orthodox faith.”

Saint Ambrose, Doctor, 340-397: “Could not Christ, who confided to him the Kingdom by His own authority, have strengthened the faith of the one whom He designated a Rock to show the foundation of the Church?”

Saint Optatus of Milevis to the Donatists: “How can you pretend to have the keys of the Kingdom of Heaven, [you] who sacrilegiously fight against the See of Peter by your presumption and impudence?”

Saint Jerome as quoted by Pope Benedict XVI: “This is what Jerome wrote: ‘I decided to consult the Chair of Peter, where that faith is found exalted by the lips of an Apostle; I now come to ask for nourishment for my soul there, where once I received the garment of Christ. I follow no leader save Christ, so I enter into communion with your beatitude, that is, with the Chair of Peter, for this I know is the rock upon which the Church is built’ (cf. Le lettere I, 15, 1-2).”

Pope Saint Damasus I, 366-384: “The First See, therefore, is that of Peter the Apostle, that of the Roman Church, which has neither stain nor blemish nor anything like it.”

~ These repeated teachings that the Roman Pontiff and his See are unsullied, unblemished, never fail in faith, etc. clearly indicate that the Roman Pontiff, in his exercise of the Keys of Peter, cannot err gravely in doctrine or discipline. And this is one of the effects of the charism of truth and never-failing faith. Another effect is that the Roman Pontiff himself is free from teaching or committing heresy. And yet another is that the Church is confirmed in Her indefectibility.

Pope Saint Damasus I, the Roman Synod of 378, to the emperors Gratian and Valentinian II: “Certain bishops, unworthy pastors, have carried their insolence and contempt to the point of refusing obedience to the Bishop of Rome.”

Saint Augustine: “Roma locuta est; causa finita est [Rome has spoken; the case is closed].”

Saint Augustine: the Roman Church, “in which the ruling authority of the Apostolic See has always held firm.”

Saint Peter Chrysologus, Doctor, 406-450, Bishop of Ravenna: “We exhort you, Honorable Brother, that you would obediently attend to that which has been written by the Pope of the city of Rome because Blessed Peter, who lives in his own See and presides there, is in charge of all those seeking the truth of faith.”

~ It is the ancient and constant teaching of the Church that Saint Peter lives, presides, and exercises judgment in the Apostolic See under every Roman Pontiff. This teaching is a corollary to the dogmas of the indefectibility of the Apostolic See and the never-failing faith of each Roman Pontiff. Peter can only have such a role, from eternity in Heaven, by the grace of God, if the Apostolic See and the Roman Pontiff is indefectible and never-failing in faith. A Pope can sin personally and gravely, but his decisions under the Keys of Saint Peter are ever protected by Christ, with the constant intercession of the first Roman Pontiff, Saint Peter.

See this link for a list of quotes teachings that Peter presides over the Apostolic See.

~ The First Vatican Council also taught that Peter presides over the Church in each of his successors, the Roman Pontiffs, and that therefore each Pope is preserved in truth and in a rock-like faith:

Vatican I: “For no one can be in doubt, indeed it was known in every age that the holy and most blessed Peter, prince and head of the apostles, the pillar of faith and the foundation of the Catholic Church, received the keys of the kingdom from our lord Jesus Christ, the savior and redeemer of the human race, and that to this day and for ever he lives and presides and exercises judgment in his successors the bishops of the Holy Roman See, which he founded and consecrated with his blood.

“Therefore whoever succeeds to the chair of Peter obtains by the institution of Christ himself, the primacy of Peter over the whole Church. So what the truth has ordained stands firm, and blessed Peter perseveres in the rock-like strength he was granted, and does not abandon that guidance of the Church which he once received [47].”

Footnote 47 above reads: Leo I, Serm. (Sermons), 3 (elsewhere 2), ch. 3 (PL 54, 146).

~ Since Saint Peter lives, presides, and exercises judgment IN HIS SUCCESSORS, and since he perseveres in rock-like faith and does not abandon the Church or the Apostolic See — all this occurring by the prevenient grace of God promised by Christ [Lk 22:32] — each Roman Pontiff cannot fail in faith and cannot lead the Church astray with grave errors in the exercise of the Keys of Peter over doctrine and discipline.

Pope Saint Zosimus, 417-418: “the tradition of the Fathers attributed so much authority to the Apostolic See that no one dared to challenge its judgment and has always preserved it through canons and regulations … such great authority belongs to Us that no one could argue again with Our decision….”

Pope Saint Boniface I, 418-422: “No one has ever boldly raised his hands against the Apostolic Eminence, from whose judgment it is not permissible to dissent; no one has rebelled against this, who did not wish judgment to be passed upon him.”

Pope Saint Boniface I: “there is to be no review of our judgment. In fact, it has never been licit to deliberate again on that which has once been decided by the Apostolic See.”

~ This principle is violated many times today by the papal opponents. They put their own judgment and that of their beloved ideological subculture (in which they place their faith instead of in the Pope and body of Bishops) above the teaching and authority of the Apostoli See.

Pope Saint Boniface I, to the bishops of Thessaly: “It is therefore certain that this Church [the Roman See] is to the Churches throughout the world as the head to its members. If anyone cut himself off from this Church, not being in union with her, he is outside the Christian religion.”

Pope Saint Celestine I, 422-432: “The sanctions of the blessed and Apostolic See may not be violated.”

Pope Saint Leo I: “The order of truth remains; blessed Peter, keeping the strength of the rock, does not abandon the helm of the Church. Whatever We do rightly is his work, whose power lives in his See…. In the person of My lowliness he is seen, he is honored, in whom remains the care of all pastors and of the sheep of their charge. His power does not fail, even in an unworthy heir.”

Pope Saint Gelasius I, 492-496, epistle to the Emperor Anastasius: “This is what the Apostolic See guards against with all her strength because the glorious confession of the Apostle is the root of the world, so that She is polluted by no crack of depravity and altogether no contagion. For if such a thing would ever occur (which may God forbid and we trust cannot be), why would we make bold to resist any error?”

~ The Apostolic See can never be polluted by any crack of depravity or contagion, which are figures indicating that grave errors in doctrine and discipline, especially heresy, cannot occur in the See of the Roman Pontiff. And this is explained, again and again, in other sources show herein, as being due to the prayer and promise of Christ in Luke 22:32, that of a never-failing faith for Peter and his successors.

The example of Pope Vigilius, d. 555, as related by Saint Bellarmine: “It happened a little afterward, that [Pope] Silverius died and Vigilius, who to that point sat in schism, now began to be the sole and legitimate Pontiff for certain through the confirmation and reception by the clergy and the Roman people. From this time neither error nor feigning of error was discovered in Vigilius, but rather, supreme constancy in the faith even to death, as it shall appear. For he received with the pontificate the strength of faith and he was changed from a weak chaff into the most solid rock.”

~ Pope Vigilius, before becoming the legitimate Pope, was a schismatic, heretic, and antipope. He was forcibly installed in Rome as an antipope by the heretical emperor. And when the true Pope, Saint Silverius, died, Vigilius was accepted as the true Pope, without an election, by the body of Bishops. Then, as Saint Robert Bellarmine, Doctor of the Church, explains, Vigilius was converted from grave error, schism, heresy, and faithlessness, into “the most solid rock”. For upon becoming Roman Pontiff, he was converted to have a never-failing faith, just a Christ promised to Peter and his successors: “But I have prayed for you, so that your faith may not fail, and so that you, once converted, may confirm your brothers.” [Lk 22:32] Thus, any necessary conversion is accomplished, in every Roman Pontiff upon the start of his Pontificate, to vanquish any heresy, schism, other grave errors, and to convert him to have a never-failing faith.

~ The case of Vigilius shows that even an antipope and manifest heretic, upon becoming the true Pope, has the charism of truth and never-failing faith and is converted from anything to the contrary.

Pope Pelagius II, 590 AD, writing to the Bishops of Istria: “For you know how the Lord in the Gospel declares: ‘Simon, Simon, behold Satan has desired you that he might sift you as wheat, but I have prayed to the Father for thee, that thy faith fail not, and thou, being converted, confirm thy brethren.’ See, beloved, the truth cannot be falsified, nor can the faith of Peter ever be shaken or changed.”

Pope Saint Gregory I (the great), Doctor, 590-604: “Who does not know that the whole Church was strengthened in the firmness of the Prince of the Apostles, to whom it was said, ‘Upon this rock I will build my Church … and thou, being converted, confirm thy brethren?’ [Mt 16:18; Lk 22:32]”52 Saint Bellarmine: “There Gregory clearly teaches the strength of the Church depends upon the strength of Peter, and hence Peter is less able to err than the Church herself.”

~ Popes are protected from grave errors on doctrine and discipline, as well as from grave failures of faith. For each Pope is the head of the Church and the rock on which the Church is founded. The indefectibility of the Church depends in large part upon the indefectibility of the Roman Pontiff.

Saint Maximus the Confessor, 580-662: “from the incarnate Word’s descent to us, all Christian churches everywhere have held and hold the great Church that is here [at Rome] to be their only basis and foundation since, according to the Savior’s promise, the gates of Hell have never prevailed against her.”

~ Not only have the gates of Hell never prevailed over the Church, but also the gates of Hell have never prevailed over the Roman Church, which is the See of Saint Peter and his successors.

Pope Saint Agatho: “…the evangelical and apostolic uprightness of the orthodox faith, which has been established upon the firm rock of this Church of blessed Peter, the Prince of the Apostles, which by his grace and guardianship remains free from all error, the whole number of rulers and priests, of the clergy and of the people, unanimously should confess and preach with us as the true declaration of the Apostolic tradition, in order to please God and to save their own souls.”

Pope Saint Nicholas I (the great), 858-867: “If anyone condemns dogmas, mandates, interdicts, sanctions, or decrees, promulgated by the one presiding in the Apostolic See, for the Catholic faith, for the correction of the faithful, for the emendation of criminals, either by an interdict of threatening or of future ills, let him be anathema.”

Pope Saint Nicholas I: “Neither by the emperor, nor by all the clergy, nor by kings, nor by the people will the judge be judged…. The first See will not be judged by anyone….”

Pope Saint Leo IX: “Without a doubt, it was for him alone, whom the Lord and Savior asserted that he prayed that his faith would not fail, saying, ‘I have prayed for thee, etc.’ [Lk 22:32]. Such a venerable and efficacious prayer has obtained that to this point the faith of Peter has not failed, nor can it be believed that it is ever going to fail in his throne.”

~ The charism of truth and never-failing faith was given only to Peter, not to the other Apostles, and so it is handed down only to each Roman Pontiff, successor of Peter, and not to the other Bishops as individuals. (The other Bishops participate in the charism of truth and never-failing faith only as a body led by the Roman Pontiff, just as they cannot exercise infallibility, except as a body led by the Roman Pontiff.) That the faith of Peter can never fail in his throne means that no Roman Pontiff can fail in faith, as the faith of the Roman Pontiff is the faith of Peter, which is the faith of Christ. And “Christ and His Vicar constitute one only head” of the one Church [Pope Pius XII, Mystical Body of Christ 40]

Pope Pius XII: “40. 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.

“41. 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.” [Mystical Body of Christ 40-41]

There are very many more sources, documented on this long page, which prove that the Church has always taught the never-failing faith of the Roman Pontiff and his freedom from heresy and grave error.

Anyone who claims that the current Roman Pontiff has taught material heresy or committed formal heresy, or has lead the Church or the faithful astray by grave errors on doctrine or discipline, is themselves guilty of at least material heresy for contradicting the ancient constant teaching of the Church on the charism of truth and never-failing faith. This charism has been confirmed by the First Vatican Council in its clear definitive teaching.

Ronald L Conte Jr