The Aramaic word kepa meaning rock and tranliterated into Greek as Kephas is the name by which Peter is called in the Pauline letters except in Gal 2,7-8. It is translated as Petros in Jn 1, 42. The presumed original Aramaic of Jesus' statement would have been, in English, "You are The Rock and upon this rock I will build my church." The Greek text probably means the same, for the difference in gender between the masculine noun petros, the disciple's new name, and the feminine noun petra may be due simply to the unsuitability of using a feminine noun as the proper name of a male. Although the two words were generally used with slightly different nuances, they were also used interchangeably with the same meaning, "rock." Church: this word occurs in the gospels only here and in 18, 17. There are several possibilities for an Aramaic original. Jesus' church means the community that he will gather and that, like a building, will have Peter as its solid foundation. That function of Peter consists in his being witness to Jesus as the Messiah, the Son of the living God. The gates of the netherworld shall not prevail against it: the netherworld is conceived of as a walled city whose gates will not close in upon the church of Jesus, i.e., it will not be overcome by the power of death.
The keys to the kingdom of heaven: the image of the keys is probably drawn from Is 22, 15-25, where Eliakim who succeeds Shebnah as master of the palace, is given "the keys of the house of David," which he authoritatively "opens" and "shuts".
There are many instances in rabbinic literature of the binding-loosing imagery. Of the several meanings given there to the metaphor, two are of special importance here: the giving of authoritative teaching, and the lifting or imposing of the ban of excommunication. It is disputed whether the image of the keys and that of binding and loosing are different metaphors meaning the same thing. In any case, the promise of the keys is given to Peter alone. In 18, 18 all the disciples are given the power of binding and loosing, but the context of that verse suggests the that there the power of excommunication alone is intended. That the keys are those to the kingdom of heaven and that Peter's exercise of authority in the church on earth will be confirmed in heaven show an intimate connection between, but not and identification of, the church and the kingdom of heaven.