"Only prayer unlocks chains, only prayer paves the way to unity," the pope said.
Pope Francis said that both St. Peter and St. Paul were prophets who looked to the future.
He said: "Peter is the first to proclaim that Jesus is 'the Christ, the Son of the living God'. Paul, who considers his impending death, said, 'From now on there is laid up for me the crown of righteousness, which the Lord will award to me."
"Peter and Paul preached Jesus, as men in love with God," he said. "At his crucifixion, Peter did not think about himself but about his Lord, and, considering himself unworthy of dying like Jesus, asked to be crucified upside down. Before his beheading, Paul thought only of offering his life; he wrote that he wanted to be 'poured out like a libation.'"
Pope Francis offered Mass at the Altar of the Chair, which is located behind the main altar that is built upon St. Peter's tomb. The pope also prayed before the basilica's bronze statue of St. Peter, which was adorned for the feast with a papal tiara and a red cope.
During this Mass, the pope blessed the "pallium," the white woolen vestments to be given to each new metropolitan archbishop. These were made with wool woven by the Benedictine Sisters of St. Cecilia in Trastevere, and are adorned with six black silk crosses.
The tradition of the pallium dates back to at least the fifth century. Metropolitan archbishops wear the pallium as a symbol of authority and of unity with the Holy See. It serves as a sign of the metropolitan archbishop's jurisdiction in his own diocese, as well as the other particular dioceses within his ecclesiastical province.
"Today we bless the pallia to be bestowed on the dean of the College of Cardinals and the metropolitan archbishops named in the last year. The pallium is a sign of the unity between the sheep and the Shepherd who, like Jesus, carries the sheep on his shoulders, so as never to be separated from it," Pope Francis said.
The pope, who himself was also wearing a pallium during the Mass, bestowed a pallium on Cardinal Giovanni Battista Re, who was elected as the dean of the College of Cardinals in January.
The recently appointed metropolitan archbishops will receive their blessed pallia from their local apostolic nuncio.
After the Mass, Pope Francis prayed the Angelus from the window of the Vatican's Apostolic Palace with a small crowd spread throughout St. Peter's Square for the feast.
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"It is a gift to find ourselves praying here, near the place where Peter died a martyr and is buried," the pope said.
"Visiting the tombs of the Apostles will strengthen your faith and testimony."
Pope Francis said that only in giving can one become great, and said that God desires to help each Christian grow in their capacity to give life.
"The most important thing in life is to make life a gift," he said, saying this is true for parents as well as consecrated.
"Let us look to Saint Peter: he did not become a hero because he was freed from prison, but because he gave his life here. His gift transformed a place of execution into the beautiful place of hope in which we find ourselves," he said.
"Today, before the Apostles, we can ask ourselves: 'And I, how do I arrange my life? Do I think only of the needs of the moment or do I believe that my real need is Jesus, who makes me a gift? And how do I build life, on my capacities or on the living God?,'" he said. "May Our Lady, who entrusted everything to God, help us to put Him at the foundation of every day."