The following excerpt is taken from the book "On the Roman Pontiff (De Controversiis Book 1)" by St. Robert Bellarmine. Until only a couple years ago this text had not been translated into English, but thanks be to God Ryan Grant, the founder of Mediatrix Press has translated many of the great saints works. Please support Ryan and his company, it is a great gift to the church!
“Therefore, four questions must be explained to us. First: whether Peter might be that rock upon which the Church shall be founded. Second: whether that foundation might be the ruler of the whole Church. Third: whether Peter might be the one to whom the keys are given. Fourth: whether the full power to govern the Church should be understood through the keys. On the first question there are four opinions...
The fourth is of Luther and the Centuriators, that faith or the confession of faith is the rock, concerning which the Lord spoke in this place...
The fourth opinion remains, which is common among nearly all Lutherans, and at first glance appears to be confirmed by the testimony of the Fathers. Accordingly Hillary teaches: “The building of the Church is the rock of confession . . . This faith of the Church is the foundation: through this faith the gates of hell are weak against it: this faith of the kingdom of heaven holds the keys.” St. Ambrose says: “The foundation of the Church is faith.” St. John Chrysostom: “Upon this rock I will build my Church, that is faith and confession.” Likewise Cyril, explaining this citation: “I reckon he called the rock is nothing other than unshaken and firm faith of the disciple.”
Illyricus adds: “If it is founded upon Peter, and rather not upon the confession of Faith of the Church, then immediately it would have fallen. For Peter soon ran at the point of the Lord’s passion, and he fell. Moreover in the same Chapter of St. Matthew, it is said to him: ‘Get behind me Satan, you are a scandal to me, because you do not have a sense of what is of God.’ Thereupon he denied Christ a third time, and not without a great curse.”
I respond: Faith, or confession, is considered in two ways. In one way it absolutely followed itself, and without any relation to the person of Peter: in the second way with relation to Peter. In the first way it appears our adversaries would have it that faith is the foundation of the Church, but certainly they are deceived. If it were so, why didn’t the Lord say, instead of: “I will build upon this rock,” “I am building,” or “I have built my Church”? Many had already believed that he was the son of the living God, as early as the prophets, the Blessed Virgin, Simeon, Zachariah, John the Baptist, the apostles and remaining disciples.
Next, faith taken up absolutely is rightly called the foundation of justification and of all strength, as Augustine says: “The house of God is founded by belief, erected by hope, perfected by love.” But the foundation of the Church is not properly faith. There ought to be a foundation of the same kind, as well as the rest of the building. The Church is a congregation of men, just as of living stones, therefore the stone, which is the foundation, ought to be also some man, not some virtue.
Last, that pronoun this most clearly showed that through the rock faith cannot be understood absolutely: for it is referred more closely to the one named rock: next, it had been said to Simon: “You are rock,” not to faith; therefore it behooves us to accept faith in the second way is the foundation, and to say not any faith you please, but the faith of Peter, and not of Peter as a private man, but as the shepherd of the Church. It coincides with that, which we said in this regard, that Peter is the foundation.
Therefore the faith of Peter is the foundation of the Church for a two-fold reasoning. First, that on account of the merit of his faith Peter attained that he should be the foundation of the Church, as Jerome, Hilary, Chrysostom and others show on this place. Secondly, because Peter is chiefly in the very matter the foundation of the Church, that since his faith cannot fail, he ought to confirm and hold up all the others in faith. Thus, the Lord said to him: “I have prayed for thee, that thy faith should not fail, and when thou hast converted strengthen thy brethren.”
Therefore, by reasoning of his indefectible faith, Peter should be the firmest rock, sustaining the whole Church; it is the same thing to say “upon Peter” and “upon his faith” the Church was founded, and the Fathers cited speak in this manner. For St. Hilary, after he had said the faith of Peter is the foundation of the Church, and receives the keys of the kingdom, he adds on Peter himself: “He merited a preeminent place by the confession of his blessed Faith,” and a little after: “Hence, he holds the keys of the kingdom of heaven, hence, his earthly judgments are heavenly, etc.”
Therefore, as he had said, “faith is the foundation and holds the keys,” so now he says Peter by reason of his faith merited a preeminent place, that is, that he should be the head, or foundation, and should hold the keys. And he says the same thing most beautifully about Peter: “O happy foundation of the Church by the solemn decree of a new name.”
For equal reasoning St. Ambrose, where he says the faith of Peter is the foundation of the Church, he notes the same thing: “He did not refuse to his disciple the favor of this word, that he should also be Peter, who as the rock should have solidity of steadfastness and firmness of faith.”
Chrysostom explaining in both citations, why it is that the Church is built upon the confession of Peter, introduces the Lord speaking thus: I will build my Church upon you.”
Next, Cyril also says the foundation is not any faith, but that unconquerable and most firm faith of St. Peter; and he writes that Peter himself is the rock, upon which the Church is founded.
Now I respond to the objection of Illyricus, firstly with the commentary of Jerome for this chapter: when Peter was told: “Get behind me Satan” and when he denied Christ, he was not yet the foundation. Therefore the place Christ promised him, he had intended to give to him after the resurrection. Add, that Peter did not err on the faith, but was merely ignorant of something, when he was told, “Get behind me Satan,” and he was lacking in charity, not in faith, when he denied Christ. That we will teach in its proper place in the treatise on the Church.”