I'm certain you have indeed heard those lines from Matthew's Gospel (16:18-19) and repeated them many times.  The Latin version of those words is inscribed around the base of St. Peter Basilica.  Beautiful!  But biblical scholarship has taught us that what we interpret as the name "Peter" is not the correct term as Jesus was not referring to His disciple at all.  It was a perfectly ordinary noun: the Aramaic "kephas," translated into the Greek "petros," meaning 'rock' or 'stone.'  There appears no contradiction that Jesus did indeed bestow a mission upon Simon (it is confirmed by St. Mark and later by St. John as well as St. Matthew), yet the first two disagree over the actual occasion when the event occurred.  Matthew is the ONLY gospel that adds Jesus's stated reason for the choice of name ("Thou art Peter and on this rock....I will give unto thee the keys of the Kingdom of Heaven."  Scholars believe the entire last passage to be a later interpolation. 
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