Our Lord promised that the gates of Hell would never prevail over the Church, he did not promise that no pope or churchman would ever teach error.
I think it was St. John Chrysostom who said…“the floor of Hell are paved with the skulls of rotten bishops…”
If you believe Vatican 1,then you should believe that the pope will never teach errors of faith and morals ex cathedra.
“Simon, Simon, behold, Satan demanded to have you, that he might sift you like wheat, but I have prayed for you that your faith may not fail; and when you have turned again [after the denials], strengthen your brethren” (Luke 22:31-32).
“Whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven” (Matt. 16:19).
St. Irenaeus:
“For it is a matter of necessity that every Church should agree with this Church, on account of its preeminent authority [propter potentiorem principalitatem] – that is, the faithful everywhere – inasmuch as the Apostolic Tradition has been preserved continuously by those who are everywhere.” (Adversus Haereses 3:3:2)
Opatatus (c. 367 A.D.):
“In the city of Rome the Episcopal chair was given first to Peter, the chair in which Peter sat, the same who was head — that is why he is also called Cephas [Rock] — of all the Apostles, the one chair in which unity is maintained by all. Neither do the Apostles proceed individually on their own, and anyone who would presume to set up another chair in opposition to that single chair would, by that very fact, be a schismatic and a sinner… Recall then the origins of your chair, those of you who wish to claim for yourselves the title of holy Church.”
(Opatatus, The Schism of the Donatists, 2:2)
Bachiarius, monk, (fl. 420 AD):
“…none of the heresies could gain hold of or move the Chair of Peter, that is the See of faith.”
(Professio fidei, 2)
St. Cyril of Alexandria (c. 424):
“He [Christ] promises to found the Church, assigning immovableness to it, as He is the Lord of strength, and over this He sets Peter as shepherd.”
(Cyril, Comm. on Matt., ad loc.)
St. Fulgentius of Ruspe (A.D. 465-533):
“That which the Roman Church, which has the loftiest place on the earth, teaches and holds, so does the whole Christian world believe without hesitation for their justification, and does not delay to confess for their salvation”
(Letter 17, 21, A.D. 519).
St. Maximus the Confessor (ca. AD 580-662):
“The extremities of the earth, and everyone in every part of it who purely and rightly confess the Lord, look directly towards the Most Holy Roman Church and her confession and faith, as to a sun of unfailing light awaiting from her the brilliant radiance of the sacred dogmas of our Fathers, according to that which the inspired and holy Councils have stainlessly and piously decreed. For, from the descent of the Incarnate Word amongst us, all the churches in every part of the world have held the greatest Church alone to be their base and foundation, seeing that, according to the promise of Christ Our Savior, the gates of hell will never prevail against her, that she has the keys of the orthodox confession and right faith in Him, that she opens the true and exclusive religion to such men as approach with piety, and she shuts up and locks every heretical mouth which speaks against the Most High.”
(Maximus, Opuscula theologica et polemica [A.D. 650], in PG 91:144)
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