Matthew 16:17-19 marks a key moment in Peter’s life and the teaching of our Lord. Jesus just finishes commending Peter for proclaiming Jesus as the Christ, the Son of the Living God. It would only make literary sense that, unless there was an obvious transition, the verses immediately following would have something to do with that proclamation.
When Jesus says, “You are Peter, and on this rock I will build my church,” He doesn’t say it in a vacuum. It relates back to what started the conversation: “who do men say that I am” not, “who do men say that you are, Peter.” In essence Jesus is saying, “we know who you are Peter, you are a little rock. You’ve proclaimed who I am – the Christ, the Son of the Living God. Now I’m telling you I am also the foundation I will build My church upon.” He then tells the gathered apostles what the role of His church will be. “The gates of Hades will not prevail against it” indicates death and persecution will not defeat the church nor dissuade her from her mission.
Since no one comes to the Father but through Christ, He has to be the keys of the kingdom of heaven that Jesus said He would give them. “Whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven” is a beautiful picture of the ultimate purpose of the church. The church is to evangelize the lost. In the eternal scheme of things, the only ones who are bound are bound by sin. Those who are saved by the finished work of Christ on the Cross are loosed from their sins and declared free by the God of the Universe. Any other interpretation, and there are many, seem to be eisegetical and do injustice to the text.
As far as the definition and origin of the church, the Greek word literally means “called out ones.” Christ is the Head of the body, the church. The church is the bride of Christ and is made up of all believers from Pentecost until the rapture. The church originated at Pentecost with the giving of the Holy Spirit and will last until she is caught up to meet Jesus in the air at the rapture.