It is a well-known fact that Ezekiel, in addition to being a prophet, was also a priest. However, it is not usually asserted that Ezekiel also performed some kingly functions as well. For instance, as I look at the infamous passages of 16 and 23, I wonder whether or not those passages (which are surely covenantal lawsuit passages) are meant to portray Ezekiel as exercising some kingly functions in addition to prophetic. Of course, he would be acting as Yahweh’s proxy in the prosecution of the case. But who judges cases in Israel? It is true that the priests were supposed to carry out this function. However, when the kings came along, they took that role for themselves. We find Solomon being the judge in Kings. In exilic Israel, the role of judge would certainly be seen as a kingly function, not so much a prophetic or priestly one.
If this is true (and I haven’t yet done a lot of research on it to lay out the argument), then Ezekiel is a prophet, priest and king. This might help enlighten for us not only the reason why God calls Ezekiel “son of man,” but also why Jesus found the title so very appropriate for Himself. Most people tend to think only of Daniel as being the background material. However, a good case can be made that Ezekiel is more in the background of Jesus’ self-designation than Daniel, or at least that they are equal.
Daniel Block has made a strong case that the phrase in Ezekiel means “mortal human being” (or something very like: I don’t currently have Block’s book in front of me). If so, then a comparison with Daniel’s use of the phrase (which certainly points to deity) yields the following interesting result: Ezekiel’s use of the phrase points out the human side, and Daniel’s use points out the divine.
Put all these thoughts together, and you have a perfectly clear portrait of why Jesus would use the phrase to describe Himself. It is just ambiguous enough not to cause immediate riot because of blasphemy (people would remember Ezekiel’s use of it to describe himself), and yet has enough background meaning to cover not only the offices of Christ, but also His natures. Throw in the additional tidbit that Ezekiel might point to humiliation, and Daniel to exaltation (this is a very tentative point on my part), and you have the perfect set of OT backgrounds for Jesus all wrapped up in the phrase “son of man:” three offices, two states, and two natures.