I'm not a protestant, but I can tell you what I believe.
Matthew 16
14 And they said, Some say that thou art John the Baptist: some, Elias; and others, Jeremias, or one of the prophets.
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.
What God revealed to Peter is the foundation of the church. That was the point of Jesus saying it right after God revealed to Peter who Jesus is. The 'church' believes Jesus is the Christ, the Son of the living God. Those whom God reveals this truth to are the church. The gates of hell cannot hold back (prevail against) the coming of Christ's church. We storm the gates of hell and bring the truth of the gospel!