"The keys of the kingdom"
Simon Peter holds the first place in the college of the Twelve; Jesus entrusted a unique mission to him. Through a revelation from the Father, Peter had confessed: "You are the Christ, the Son of the living God." Our Lord then declared to him: "You are Peter, and on this rock I will build my Church, and the gates of Hades will not prevail against it." Christ, the "living Stone", thus assures his Church, built on Peter, of victory over the powers of death. Because of the faith he confessed Peter will remain the unshakeable rock of the Church. His mission will be to keep this faith from every lapse and to strengthen his brothers in it.
Source: Catechism of the Catholic Church (Vatican.va)