by Scott Butler, Norman Dahlgren, David Hess.
As Catholics we believe there are three authorities, the Bible, Sacred Tradition, and the Teaching Authority of the Church, known as the Magisterium. The pope is the head of the Magisterium.
We need to look briefly to the old testament to see that when a king in the Davidic line gave the keys to the kingdom to his right hand man, he was giving that person authority to speak in his place. When Jesus told Peter that he is the rock on which he will build his church and gave him the keys to his kingdom, Jesus, a Davidic king, was giving Peter authority not just a title. As each of the pope dies, another person is chosen to take his place. The new person does not just inherit a job but the authority that goes with the title.
Matthew 16:17-19
Jesus said to him in reply, "Blessed are you, Simon
son of Jonah. For flesh and blood has not revealed this to you, but my
heavenly Father. And so I say to you, you are Peter, and upon this
rock I will build my church, and the gates of the netherworld
shall not prevail against it. I will give you the keys to the kingdom
of heaven. Whatever you bind on earth shall be bound in heaven; and
whatever you loose on earth shall be loosed in heaven." (New
American Bible: study edition
So, the pope, as the head of the Teaching Authority of the church, is the man Catholics look to for spiritual guidance of our church.