According to him the Church is built upon Peter, in pursuance of the promise of Matt.16:16-19. Peter participates in everything which is Christ's; what the other apostles have in common with him they have through him. The Lord prays for Peter alone when danger threatens all the apostles, because his firmness will strengthen the others. What is true of Peter is true also of his successors. Every other bishop is charged with the care of his own special flock, the Roman with that of the whole Church. Other bishops are only his assistants in this great task.
Through the see of Peter, Rome has become the capital of the world in a wider sense than before. For this reason, when the earth was divided among the apostles, Rome was reserved to Peter, that here, at the very center, the decisive triumph might be won over the earthly wisdom of philosophy and the power of the demons; and thus from the head the light of truth streams out through the whole body.
In Leo's eyes the decrees of the Council of Chalcedon acquired their validity from his confirmation. The wide range of this theory justifies the application to him of the title of the first pope.
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