From the "Discourses" of St. Leo the Great, Pope
Disc. Fourth anniversary of his election, 2-3), PL 54, 149-151)
"Of all the men Peter alone is chosen to be the first to call all people to salvation and to be the head of all the Apostles and the Fathers of the Church. The people of God consist of many priests and pastors, but the true guide of all is Peter, under the escort of Christ supreme. Beloved, God has deigned it to make this man to share in his power to a great and marvellous extent. And if you wanted the other princes of the Church to have something in common with him, it is always through him that conveys how much the others have not denied.
The Lord asks all the apostles what people think of him and all give the same answer until it continues to be the ambiguous wording of the common human ignorance. But when the apostles were surveyed for their opinion, then the first to profess faith in the Lord was the one who was also the first in terms of apostolic dignity. He says: "You are the Christ, the Son of the living God," and Jesus replies, "Blessed are you, Simon son of Jonah, for flesh and blood has not revealed this, but my Father who is in heaven "(Mt 16, 16-17). This means ‘you are blessed, because my Father has taught you, and you're not fooled by human opinions, but you have been instructed by heavenly inspiration. My identity has not been revealed to you by flesh and blood, but by Him by whom I am the only Son." Jesus continues: "And I tell you: just as my Father has revealed to you my divinity, so will I manifest your dignity. Thou art Peter." This means that if I am the inviolable rock, "the cornerstone who has united us as one" (Eph 2: 14. 20), the foundation that no one can replace, you're a rock, because my strength will grant you an equilibrium."