20 Nor is he less zealous when, from faraway Edessa, he looks to Rome to extol the Primacy of Peter: "Hail, holy kings, Apostles of Christ," and to the choir of Apostles, "Hail, light of the world.... Christ is the light and the lampstand is Peter; the oil, however, is the activity of the Holy Spirit. Hail, O Peter, gate of sinners, tongue of the disciples, voice of preachers, eye of the Apostles, guardian of heaven, the first-born of the keepers of the keys." And in another place, "Blessed are you, O Peter, the head and tongue of the body of your brothers, the body which is joined together with the disciples, in which both sons of Zebedi are the eye. They indeed are blessed, who contemplating the throne of the Master, seek a throne for themselves. The true revelation of the Father singles out Peter, who becomes the firm rock.'' In another hymn he introduces the Lord Jesus speaking to his first vicar on earth: "Simon, my disciple, I have made you the foundation of the holy Church. I called you "rock" that you might sustain my entire building. You are the overseer of those who build a church for me on earth. If they should wish to build something forbidden, prevent them, for you are the foundation. You are the head of the fountain from which my doctrine is drawn. You are the head of my disciples. Through you all nations shall drink. Yours is that vivifying sweetness that I bestow. I have chosen you to be as a firstborn in my institution and heir to all my treasures. The keys of the kingdom I have given to you, and behold I make you prince over all my treasures."
Source: Principi Apostolorum Petro (Vatican.va)