Originally Posted by
dwashbur
Actually, it's a pun. He's been calling Simon son of Jona "Peter" (or Cephas in Aramaic) for a long time, and he's pointing out that even though he's been calling him "rocky" so to speak, his church will be built on a much bigger Rock, i.e. himself.
There's an alternate interpretation, which suggests that the "rock" he's speaking of is Peter's confession of Jesus as Messiah and Son of God. I could go with that one, too. But what he's definitely NOT saying is that Peter himself is the "rock."