Peter was a fisherman in the village of Capernaum when he decided to follow Christ. One day the apostles were in the region of Cesarea Phillipi when Jesus asked them this question:
do you say that I am?"
Simon Peter said in reply,
"You are the Messiah, the Son of the living God."
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 nether world 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." (Mt. 16:15-19)
The symbolism here is unmistakable. Peter means rock and rock here stands for foundation. The keys symbolize authority and power.
After the resurrection Christ appeared to the apostles the third time and asked Peter if he loved Him more than the others, Peter answered, "Yes, Lord, you know that I love you." He said to him, "Feed my lambs." (Jn 21:15) This expresses the purpose of Peter's authority, that is to care for the faithful Christians. This implies a threefold authority to teach, govern and sanctify.
In the nineteenth century there were some who called into question Peter's primacy and authority by saying that authority and power were given primarily to the Church as a whole and was exercised by the apostles or bishops and not by Peter and his successors. The First Vatican Council reacted by saying, "If anyone says that blessed Peter the apostle was not appointed by Christ the lord as prince of all the apostles and visible head of the whole church militant; or that it was a primacy of honour only and not one of true and proper jurisdiction that he directly and immediately received from our lord Jesus Christ himself: let him be anathema."
All the popes coats of arms since their beginning with Pope Innocent I (1243-1254) bear the symbol of the keys indicating that they trace their power to St. Peter. The Key of gold represent the Pope power to bind while the silver key indicates his power to loose. Pope Benedict XVI is the first pope to use the mitre instead of the tiara in conjunction with the keys.