Beginning with chapter two, God uses a phrase to refer to His prophet that he uses only one other time, referring to Daniel (Daniel 8:17). He uses it to refer to Ezekiel however 93 times.
A “son of man” is, basically, just another way of saying “man,” for that is what a “son of a man” is. Why does God do this?
It is a reminder to the prophet and to the readers of the prophet that he, and they, are just that: mortal. Their only real hope in life is in the company of He who is decidedly not mortal: God. Unfortunately, what is going to happen in Ezekiel is that God is going to move His presence away from His people, and the result will be only lament, warning, and woe.
The phrase “son of man” takes on a new meaning in the New Testament.
Ezekiel, though he is but a man, is a man filled with the Spirit of God. He is special to God, and though it looks like God is just calling him “man,” the fact that God keeps on doing it, and virtually doesn’t do it to anyone else, gives Ezekiel a certain status no one else has. It makes him unique. When this phrase is used in the New Testament to refer to Jesus, it likewise conveys to him a unique status, one filled with the Spirit, chosen, and directed by God. He is a man, but much much more than that.