There is a play upon words here. In the original Greek it is, You are Petros [a little piece of rock, a pebble], and upon this petra [bedrock] I will build my church.
What I meant is that Jesus is the rock, petra, on which the Church is built. Peter is just a pebble, petros!
Lets look at the passage containing that verse. Jesus asks who they (the Apostles) think He is.
Matthew 16:15 He saith unto them, But whom say ye that I am? 16 And Simon Peter answered and said, Thou art the Christ, the Son of the living God. 17 And Jesus answered and said unto him, Blessed art thou, Simon Barjona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven. 18 And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it.
When Jesus makes the statement and upon this rock I will build my church He is referring back to who the Apostles say He is, not to Peter. He (Jesus) is the rock upon which the church is built.