As they were coming down the mountain may need to be rendered “As Jesus and his disciples were coming down the mountain.”
Jesus commanded them: for other commands to silence see 8.4; 9.30; 12.16; 16.20. This is the last time that Jesus issues such a command in this Gospel.
The vision (Good News Translation “this vision you have seen”): this is the only place in the Gospels where the word vision occurs; in the Marcan parallel (9.9) the text reads “what they had seen.” Die Bibel im heutigen Deutsch and New International Version render vision as “what you have seen.” The same thing is done also by Phillips and Barclay, though they both shift to indirect discourse: “Jesus warned them not to tell anyone about what they had seen” (Phillips) and “Jesus gave them strict orders not to tell anyone what they had seen” (Barclay). Visions and dreams were acceptable means of divine revelation (see 1.20; 2.12, 13, 19). The distinguishing factor is the time element: visions may take place at any moment; dreams are reserved for the time when a person is sleeping. There will be many languages where vision is a word known well enough that translators will more likely follow the Good News Bible model than Phillips or Barclay (cited above).
For Son of man, see the discussion at 8.20.
Is raised from the dead: see comments at 16.21 and 14.2. Good News Translation and New English Bible follow the same interpretation as Revised Standard Version, since the Greek verb for raised is passive in form. The understanding that the verb has an active meaning, “has risen from death,” is the exegesis adopted by Bibel im heutigen Deutsch, 1st edition, Luther 1984, New Jerusalem Bible, and New American Bible, based on the opinion of some scholars that Matthew intentionally and regularly used the same passive form for resurrection as the verb for “awaken” (as in 1.24; 25.7).
Translators may have to restructure this command: “Don’t tell anyone about this vision you have seen before the time when God raises the Son of Man from death” or “You must not tell anyone about what you saw here until after the Son of Man has been raised from death.”
Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .