**The key to Peter is just that... the Keys.**
Peter used the ‘keys’ alright. He was the preacher that was present when the Holy Ghost was initially poured out to the three segments of the population; ‘opening’ the doors to the Jews (Acts 2), the Samaritans (Acts 8), and the Gentiles (Acts 10).
Was Simon Peter the first to discover that Jesus was the Christ? No:
Andrew realized that Jesus was the Christ before Peter: “He first findeth his own brother Simon, and saith unto him, We have found the Messias, which is, being interpreted, the Christ.” John 1:41.
It isn’t that Peter was more of a man than others or had unshakeable faith (clearly)... he was given a special commission by Christ to feed His flock. He was chosen to be servant of the others just as the Pope is called the “servant of the servants of God.”