37 This faith it is which is the foundation of the Church; through this faith the gates of hell cannot prevail against her. This is the faith which has the keys of the kingdom of heaven. Whatsoever this faith shall have loosed or bound on earth shall be loosed or bound in heaven. This faith is the Father's gift by revelation; even the knowledge that we must not imagine a false Christ, a creature made out of nothing, but must confess Him the Son of God, truly possessed of the Divine nature.
What blasphemous madness and pitiful folly is it, that will not heed the venerable age and faith of that blessed martyr, Peter himself, for whom the Father was prayed that his faith might not fail in temptation; who twice repeated the declaration of love for God that was demanded of him, and was grieved that he was tested by a third renewal of the question, as though it were a doubtful and wavering devotion, and then, because this third trial had cleansed him of his infirmities, had the reward of hearing the Lord's commission, Feed My sheep, a third time repeated; who, when all the Apostles were silent, alone recognised by the Father's revelation the Son of God, and won the pre-eminence of a glory beyond the reach of human frailty by his confession of his blissful faith!
What are the conclusions forced upon us by the study of his words? He confessed that Christ is the Son of God; you, lying bishop of the new apostolate, thrust upon us your modern notion that Christ is a creature, made out of nothing. What violence is this, that so distorts the glorious words? The very reason why he is blessed is that he confessed the Son of God. This is the Father's revelation, this the foundation of the Church, this the assurance of her permanence. Hence has she the keys of the kingdom of heaven, hence judgment in heaven and judgment on earth.
Through revelation Peter learned the mystery hidden from the beginning of the world, proclaimed the faith, published the Divine nature, confessed the Son of God. He who would deny all this truth and confess Christ a creature, must first deny the apostleship of Peter, his faith, his blessedness, his episcopate, his martyrdom. And when he has done all this, he must learn that he has severed himself from Christ; for it was by confessing Him that Peter won these glories.
Source: On the Trinity (New Advent)