“Don’t tell anyone what you have seen until the son of man has been raised from the dead.” (Matthew 17:9)

This was spoken by Jesus as he and Peter, James and John were walking down from the mountain after they had witnessed hearing God’s voice, and Jesus had spoken with Moses and Elijah.

“Don’t tell anyone what you have seen..."

It is understood from his statement that Jesus knows people may not understand what happened on the mountain very easily, and it could inflame things. As such, the information is best suited for later understanding.

"...until the son of man..."

Remember that "son of man" is a mistranslation of the Greek phrase, υἱὸς τοῦ ἀνθρώπου. The word υἱὸς can only mean "son" in the context of a physical family, and the lexicon confirms that it also relates to a follower or servant ("used to describe one who depends on another or is his follower.")

Furthermore, the word ἀνθρώπου can mean "man," or "mankind" or "humanity."

Thus the more appropriate translation of υἱὸς τοῦ ἀνθρώπου is:

"Servant of Humanity"

This is appropriate, because Jesus was serving all of humanity with his teachings.

"... has been raised from the dead.”

There is a misunderstanding among ecclesiastical sectarian institutions regarding the concept of “raised from the dead.” Most ecclesiastical theologians interpret this statement to mean the three-day disappearance of Jesus’ body, and the sudden appearance of his form to his disciples.

The phrase "raised from the dead" is being translated from the Greek phrase ἐκ νεκρῶν ἐγερθῇ. The word ἐκ means "from." The word means can mean "lifeless" or "dead" when used literally, yes. But metaphorically - which Jesus was speaking, according to the lexicon, the word means "spiritually dead" or "inactive as respects doing right."

And ἐγερθῇ means "to arouse, cause to rise" according to the lexicon.

Now are we to believe that Jesus is talking about himself being dead at some point? No. Jesus did not recognize that we die when our body dies:
"Do not be afraid of those who kill the body but cannot kill the soul." (Matt. 10:28)
In fact, Jesus' entire teachings were based upon the foundation that after the death of the body we move on - and should we dedicate our selves to the Supreme Being - we return to the spiritual realm.

Who will return to the spiritual realm? A decomposing dead body?

For hundreds of years humans have been digging up various remains to study ancient history. Frequently, we will even dig up a grave to study a person’s cause of death. Sometimes we even discover situations where people were buried in fields a few years ago. In every case, we find that the human body simply decomposes: No differently, in fact, than an animal body decomposes. We also find no difference in the decomposition between a ‘Christian’ and a non-'Christian' either. Every body decomposes equally once the spirit leaves the body. This is called death.

In other words, Jesus is not talking about himself dying at all. He is speaking of himself "rising" or leaving the physical world - the place of the spiritually dead.

To this we can reference another statement describing Jesus' thoughts about the physical world:
“Follow me, and let the dead bury their own dead.” (Matt. 8:22)
Here we see again how Jesus is describing persons who are spiritually dead. They are focused upon the forms and things of the temporary physical world. They are identifying themselves with the physical body, and are thus spiritually dead.

To be spiritually dead means to think that this body is "me." We are not these physical bodies, however. We are the spiritual living beings within this physical body.

Just as a person sits down within a car, we sit within the vehicle of the physical body.

This temporary physical body is dead matter without the spiritual lifeforce that drives it. When the living spirit leaves the body, the body dies. In other words, the body is animated by the spiritual living being.

Thus, physical matter is essentially dead, and those who dedicate themselves to the matter of the physical world are considered spiritually dead.

So in the above statement, Jesus is telling his disciples to not reveal what happened until after his body dies and he - the spiritual being - returns to the spiritual world - being "raised from the dead".

 (For a translation of Jesus' statements from the Book of Matthew without institutional sectarian influence, see the Gospels of Jesus  - translated from the original Greek texts.)