This quotation is known from St. Francis de Sales. We have to acknowledge that one or two authors writing about matters of faith and doctrine are not the entire traditional Catholic Magisterium, furthermore, they are also not speaking as a Council or on behalf of the Council like a Pope.
It is only their opinion. We have to distinguish between the doctrine of faith or dogma and the opinion of theologians. Hence, what St. Francis de Sales said is only an opinion. It has never occurred in the history of the Church for a Pope to be declared a formal heretic and consequently be removed from office as a result.
Therefore, this is a very strong argument or opinion that this theory, whether it came from St. Francis de Sales or St. Robert Bellarmine, is not the constant teaching and meaning of the Magisterium of the Church. This theory was not proclaimed by any Pope, therefore, it is only an opinion even from a saint because St. Francis de Sales is not infallible. I think it is also impossible in a practical way that a Pope will lose his office. We have to use our common sense and logic.
There is no practical solution even if a Pope will lose his office, if so, there will be a gathering of Cardinals and other high-ranking members of the Church for them to discuss if the Pope is truly a heretic. This discussion might lead to division because the other party thinks the Pope is a heretic while the other thinks otherwise.
Furthermore, the people who think the Pope is truly a heretic might elect a new Pope and this happened in the 14th-century great schism; wherein, there were three Popes. This mentality will further damage and confusion in the Church. If we do happen to have a Pope who is spreading errors, we just have to bear with him because he will not live forever, only the Church is eternal and more powerful than a single Pope.
God will always be the head of the Church. We don't need to follow the Pope who spreads error, we just have to return or follow the catechisms and wait for a new Pope. Do not worry for God will always provide for His church, it has always been His church, not ours. Because the Church encompasses far more than a single Pope, as I indicated previously, it is erroneous to believe that the Pope embodies the whole Church.
If a Pope declares matters of faith, morals, and doctrine, he cannot proclaim a heresy, this is known as ex cathedra, and it is the extension of his infallibility. In other cases, when not speaking in ex-cathedra, especially non-definitive teachings, the Pope can commit an error. Because it would contradict the idea of the Pope's infallibility, the Pope won't declare these things for us to believe.
God will never allow this to happen otherwise the gates of hell will prevail in the Church. Thus, we need to have more faith in divine providence because the Church is ultimately in God's hands.
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