Jesus, before continuing with His revelation to His apostles, takes a moment to compose Himself again. He has just thwarted another of Satan’s attempts to tempt Him into abandoning His Father’s plan and doing things the easy way. And Peter, His Peter, is the one Satan used to try to trick Him. The Rock whom Jesus has just commended for following Him steadfastly became a stone that tried to trip Him up. He closes His eyes and offers a prayer of thanksgiving to His Father, who has kept Him strong and helped Him to see through the trap. He opens His eyes and looks at Peter. Poor Peter is sitting with his head down, white-faced and trembling. He doesn’t understand what has just happened. Jesus says, “Peter.” Peter slowly, fearfully, raises his eyes to his Messiah. He doesn’t see condemnation or anger, only love and compassion. Sitting up straight now, he once again gives Jesus his full attention. Jesus tells them, “I tell you these things so that you will be prepared for their coming. This must happen to fulfill My Father’s plan.” The apostles don’t know what to think. They convince themselves that Jesus is once again speaking in a parable, that His words are just a metaphor. Because otherwise, what are they going to do? What are they supposed to believe now? But, no time to think about that now. They follow Jesus as He rises and leaves their secluded area, to find a group of people waiting for them near the mountain. No matter where they go, the people always follow. The apostles are encouraged by this, for if the people love Him this much, how will they turn against Him in Jerusalem? Jesus welcomes the crowd and climbs a little way up the mountain to teach them.
Matthew 16:21-23, Mark 8:31-33, Luke 9:21-22, http://biblehub.com/commentaries/matthew/16-23.htm