(Sorry but I had the repost my comments, its was drowned in another discussion)
Fr Pfeiffer sermon is no good at all! During this sermon, Fr. says many errors and calumnies that were refuted before and during the Vatican Council (1870) by great Catholic authors.
I give you an example. Between 18:27 and 19:27, Fr. is talking about the denial of Saint Peter explaining that the first Pope denied Our Lord, so a pope can fell in heresy. That is not true! This is a calumny that was refuted many times before and Fr. Pfeiffer is refuted by the great Dom Guéranger in his book the The Papal Monarchy
This book is not just merely an opinion. It was giving a brief by Pius IX himself saying:
"Brief from Pope Pius IX
To Our dear son Prosper Guéranger, of the Benedictine Congregation of France, Abbot of Solesmes
PIUS IX, SUPREME PONTIFF.
Dear son, greetings and Our apostolic blessing (...)
(...) For this reason they boldly advance certain pernicious doctrines which have been condemned repeatedly, as if there could be no doubt about them, or as though they could be freely taught, at least; from old proponents of these doctrines they scrape together historical quibbles, mutilated passages, calumnies hurled at the Roman Pontiffs, and all sorts of sophistries. With the utmost impudence they bring all these things up again, completely setting aside the solid arguments with which they have been refuted a hundred times. Their purpose is to agitate minds and to incite the men of their faction and the ignorant crowd against the general consensus of the others."
You can read the brief of the Pope on this link:
http://www.loretopubs.org/papal-monarchy-the.html I didn't find the book in English on the web, but in French at page 97-98 Dom Guéranger refute this Gallican lie that Saint Peter the Pope denied Jesus because he was no Pope at that time, he had only the promise of the Papacy.
Our Lord talk to him in the future when saying: "And I say to thee: That thou art Peter; and upon this rock I will build my church, and the gates of hell shall not prevail against it." Saint Peter was officially Pope after the Resurrection when Our Lord talks to him at the present tense: " Feed my lambs, Feed my sheep".
For those knowing French:
http://www.liberius.net/livres/De_la_monarchie_pontificale_000000116.pdfNever, before 1958, did a Pope been an heretic. If someone says so it is because they are repeating lies and calumnies that was first invented by the Schismatic Greeks, repeated by the Renaissance men, the Encyclopedists of the XVIIIth century and the Gallicans and sadly by the SSPX today. I never read or heard Archbishop Lefebvre saying those refuted calumnies, but the SSPX has always been more liberal that its founder!