Matthew 17:9-13 (ESV)
And as they were coming down the mountain, Jesus commanded them, "Tell no one the vision, until the Son of Man is raised from the dead."  And the disciples asked him, "Then why do the scribes say that first Elijah must come?"  He answered, "Elijah does come, and he will restore all things.  But I tell you that Elijah has already come, and they did not recognize him, but did to him whatever they pleased. So also the Son of Man will certainly suffer at their hands."  Then the disciples understood that he was speaking to them of John the Baptist.
Every time I read this I’m left wondering why it was that Jesus tells them not to tell anyone. Perhaps he was afraid everyone would believe the disciples. This could have been quite problematic actually. Jesus was always at pains not to draw too much attention to himself, even as he performs miracles and teaches the masses. He is constantly running from the crowds. The problem? They don’t want him to go to the cross. Jesus is single minded in his focus. He will not be an earthly messiah, and earthly king, he will die on the cross for the sins of mankind. He will save us, despite all our attempts to save him.