The importance of the popes in Church history and in the governance of the Church cannot be overestimated. While Our Lord established the Apostles, and their successors the bishops, as pastors of His Church, exercising His priestly, prophetic and kingly office toward those whom they serve (Mt. 18:18, 28:18-20), He set Peter as chief of the apostles, exercising Christ's own authority over the whole Church (Mt. 16:13-18). The Pope is titled the Vicar of Christ, for this reason, in analogy to the role of the vizier in the Davidic Kingdom of Israel. He is the prime minister who exercises the King's authority and guards His possessions "until He comes again."
In the case of the Church, these are the teachings of Christ contained in the deposit of the faith, the treasury of the merits of the Redemption dispensed through the sacraments, and the pastoral care of the sheep. In this way, the Pope serves as the principle of unity for the bishops of the world, and thereby, for all the faithful dispersed throughout the world, guaranteeing unity in the faith, unity in the sacraments and unity of communion of Christ's flock, the ecclesia (assembly) of all the redeemed. In this way the Lord's prayer at the Last Supper is realized, “that they may all be one, as you, Father, are in me and I in you, that they also may be in us, that the world may believe that you sent me” (John 17:23).