Jesus is building His church on a rock (Mat 16:18-20). The church is made up of all the people who have believed in Jesus as the Christ or Messiah, the Son of God. That the church is built on a rock indicates its indestructability. As the man in one of Jesus’ earlier parables built his house on a rock which stood through the storm (7:24-25) so the church stands forever despite persecution and tribulation. Not even death or the gates of Hades can prevail against the church. Since Christ was raised from the dead, never to die again, so all His people who die will be raised unto eternal life. The church is built on a rock!
What or who this rock is has been the source of debate. It is probably best to see the rock as the apostle Peter who is the rock or foundation of the church because he seems to the first to confess Jesus as the Messiah, the Son of God. So, the church is built on Peter not as a man, but because of his confession of faith. It is also true that not just Peter, but the apostles as a group are the foundation of the church (Eph 2:19-22). The apostles are the foundation of the church because God’s revelation came through them to the church. It is on the truth God revealed to them that the church is built. The great confession of faith made by Peter that Jesus is the Christ, the Son of the living God (vs.16), was revealed to him by God the Father (vs.17). It is because Peter and the apostles were given God’s revelation that they have authority. That authority is seen in the keys of the kingdom of heaven and the prerogative to bind and loose on earth what has been bound or loosed in heaven (vs.19, cp. 18:18). It is the revelation of Jesus as God’s Son that the apostles preached. This revelation is the key to the kingdom of heaven in that those who believe are admitted!