As they were coming down the mountain, Jesus commanded them, “Do not tell anyone about this vision until the Son of Man has been raised from the dead.”
Matthew 17:9. And as they were going down from the mountain. We have said that the time for making known the vision was not yet fully come; and, indeed, the disciples would not have believed it, if Christ had not given a more striking proof of his glory in his resurrection.
We have here the story of Christ's transfiguration; he had said that the Son of man should shortly come in his kingdom, with which promise all the three evangelists industriously connect this story; as if Christ's transfiguration were intended for a specimen and an earnest of the kingdom of Christ, and of that light and love of his, which therein appears to his select and sanctified ones.
Commenting on Matthew 17:1-13
And as they came down from the mountain,.... Where all these things had been transacted, Jesus charged them, saying, tell the vision to no man: by the "vision" is meant, as it is explained in Mark, "what things they had seen"; as Moses and Elias, and the bright cloud that overshadowed them, and Christ transfigured before them, in a surprising, glorious manner.