Matthew 17:8-9 “And when they had lifted up their eyes, they saw no man, save Jesus only. And as they came down from the mountain, Jesus charged them, saying, Tell the vision to no man, until the Son of man be risen again from the dead.”
There are times when we are tempted to tell people too much of the Truth too soon. The significance of the Transfiguration could be properly interpreted only after the Resurrection. If people heard all of the Truth about it too soon it would only give the people a false hope about Jesus overthrowing the government of Rome and becoming a king, rather than going to the cross to die for our sins.