There are two shocking conversations in Matthew 16. In the first Peter proclaims Jesus is God Savior. A soaring high point with this affirmation from Jesus–
Matthew 16:17-19 (NIV)
Jesus replied, “Blessed are you, Simon son of Jonah, for this was not revealed to you by man, but by my Father in heaven.  And I tell you that you are Peter, and on this rock I will build my church, and the gates of Hades will not overcome it.  I will give you the keys of the kingdom of heaven; whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven.”
Then in quick narrative succession, Jesus denounces Peter as his spiritual enemy for not being supportive enough of Jesus’ impending crucifixion.
The very high and the very low are very connected.
Unless Jesus dies to give Peter life, Peter ain’t gonna be no rock.
He gives us his life. He gives us ransom.
And with this priceless gift he expects us to…batter down the very stronghold of hell.
Tall order for a grimy fisherman.