Matthew 17:9

‘And as they were coming down from the mountain, Jesus commanded them, saying, “Tell the vision to no man, until the Son of man be risen from the dead.” '

Jesus makes clear, as they descend from the mountain, that the vision had been meant for them and them alone, until after His resurrection. The last thing He wanted was for the crowds to be stirred up to do something foolish. He did not want to be the cause of a revolution. And again He reminds them that as the Son of Man He must arise from the dead.