Mark has reported a series of miracles--walking on the water, several healings, two feedings of large crowds.
Who can do these things?
Jesus asks his followers, "Who do people think I am?" The disciples give a list of forerunners to the Messiah. Then Jesus asks "Who do you think I am?"
Peter answers for them, "You are the Messiah." Jesus instructs them not to tell anyone.
The crowds are ready to know that the Messiah is coming, but not ready to realize that he is here, among them.
They are not aware of what being the Messiah means. Not just victory. Not just winning over oppressors. And it's time for those closest to Jesus to begin to learn this.
Jesus begins to teach them what is going to happen--not just the healings and feedings and water-walking, but also suffering, rejection, and even death.
Peter doesn't like this kind of talk and tries to persuade Jesus to back off some. Jesus is adamant.
Jesus speaks not only to the disciples but to the crowds, "If you want to follow with me, deny yourself, take up your cross, and follow me."
He's talking to us.