The Roman Catholic Church has just elected a new Pope to be head of the church. They see the Pope as the successor to Peter. They think Peter is the 'rock' mentioned in the following passage.
...Matthew 16:18: And I (Jesus Christ) 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. (kjv)
However the name Peter is 'pétros' which means a small stone or pebble. The original word for rock here is 'pétra' which means a cliff or boulder. If you read what is written before this verse, we see the 'rock' is not referring to Peter, but to Christ! Peter's confession of Christ is the focus of this conversation.
Matthew 16:16-17: And Simon Peter answered and said, Thou art the Christ, the Son of the living God. 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... (kjv)
Jesus is saying something like this: Hey Peter! You are just a small stone in comparison to me; I am a huge rock! Christ is the rock 'pétra', not Peter 'pétros'. Christ is clearly represented as a rock in the following passage.
1 Corinthians 10:4: And did all drink the same spiritual drink: for they drank of that spiritual Rock that followed them: and that Rock was Christ. (kjv)