Creation of an Institution?

Mark 8:29-30
(29)  And he asked them, "But who do you say that I am?" Peter answered him, "You are the Christ."
(30)  And he strictly charged them to tell no one about him.

(29)  καὶ αὐτὸς ἐπηρώτα αὐτούς, Ὑμεῖς δὲ τίνα με λέγετε εἶναι; ἀποκριθεὶς ὁ Πέτρος λέγει αὐτῷ, Σὺ εἶ ὁ Χριστός. 

(30)  καὶ ἐπετίμησεν αὐτοῖς ἵνα μηδενὶ λέγωσιν περὶ αὐτοῦ.

I have often heard that Matthew 16:18 is the proof text for the establishment of the papacy.  This is the parallel passage where Jesus has the same conversation with Peter.  However, there is no commentary about how Peter is the "rock" and upon this rock Christ would build His church.  

I don't want to make too strong of an argument from silence, but it has always seemed to me that such an important doctrine would be clearly spelled out if indeed that is what Matthew 16:18 was all about.  Mark is known for his brevity, but I would think that he would have repeated the command to establish Christ's church on earth.

Instead we simply get Peter's confession.  It doesn't take much Greek to appreciate the statement Σὺ εἶ ὁ Χριστός.  Jesus indeed is the Christ.  Incidentally, when I read ἐπετίμησεν I think of the glosses "rebuke" or "warn."  Jesus was serious about them keeping this quiet until the time was right.

Sadly, I'm afraid that many of us operate as if this was still in effect.  Now it is our job to go and make disciples of all nations.  Let's be sure to do that instead of keeping quiet.