You MUST KNOW that refers to the O.T.?ha, except the "Son of Man" part, i guess?
I can explain it if I have to...
The Son of Man refers to the Messiah. It was a Messianic title.
It comes from Daniel 7:13-14
“In my vision at night I looked, and there before me was one like a son of man, coming with the clouds of heaven. He approached the Ancient of Days and was led into his presence. He was given authority, glory and sovereign power; all peoples, nations and men of every language worshiped him. His dominion is an everlasting dominion that will not pass away, and his kingdom is one that will never be destroyed.”
This does describe Jesus, as many O.T. prophecies did.
Also, this is true because Jesus was a Son of man. (Mary).
So it's true in more ways than one.