"Jesus and his disciples went on to the villages around Caesarea Philippi. On the way he asked them, 'Who do people say I am?' They replied, 'Some say John the Baptist; others say Elijah; and still others, one of the prophets.' 'But what about you?' he asked. 'Who do you say I am?' Peter answered, 'You are the Christ.' Jesus warned them not to tell anyone about him." NIV translation
Here, we see the fundamental question that divides the world today. Who was/is Jesus? There are those who say He was a great man like John the Baptist. There are those (Muslims) that say He was a prophet. Then, there are Christians (like Peter) who acknowledge Him as the Son of God and Savior of the world.
Why did Jesus tell them to keep it to themselves? It was not the proper time for it to be revealed and it was not the manner in which God was going to reveal it. Talk is cheap and so God was going to reveal Jesus as the Christ when He died on the cross and rose again.
"He then began to teach them that the Son of Man must suffer many things and be rejected by the elders, chief priests, and teachers of the law, and that he must be killed and after three days rise again." NIV translation
Now that they knew who He was, Jesus began to teach them about the things that were to come.
He explained that the religious system would reject Him even to the point of killing Him but that He would rise again in victory.
It is the same today, in that, man has tried to make the church a religious system and in the process have rejected the teaching of Jesus. The old laws have been brought back into the church and new ones have been added with every denomination.
"He spoke plainly about this, and Peter took him aside and began to rebuke him. But when Jesus turned and looked at his disciples, he rebuked Peter. 'Get behind me, Satan!' he said. 'You do not have in mind the things of God, but the things of men.'" NIV translation
Peter could not accept the things that Jesus was saying and began to correct Him. Jesus corrected Peter and even called him Satan. How could this be? The simple fact of the matter is that there are two sides to the battle that is going on even to day. You are either in tune with God's plan or you are working for the devil. What do you have your mind set on? If its not the "things of God", then, you are on the wrong team.