The "Son of Man" motif is central to Jesus' self-understanding and of critical importance for a narrative-historical reading of the New Testament. As J.D.G. Dunn says:
After 'the kingdom of God/heaven' there is no phrase so common in the Jesus tradition as 'the son of man'. Its importance within the Jesus tradition, and possibly as a key to that tradition, therefore, can hardly be exaggerated. More to the immediate point, it seems to be the nearest thing in the Jesus tradition to a self chosen self-designation.1
The history of interpretation is exceedingly, and probably unnecessarily, complex. I suggest that three patterns of usage are relevant for understanding what Jesus meant when he referred to himself as "the son of man".
1. A semitic idiom of self-reference
The expression is a common semitic idiom for a "person" and may serve as a form of self-designation ("a person like me")—Psalm 8:4 is a classic example: "what is man that you are mindful of him, and the son of man that you care for him?" But this does not account for the frequency of the expression on Jesus' lips or its narrative development in his teaching.
2. Ezekiel as the "Son of Man" who prophesies judgment against Israel
The expression is found with this idiomatic sense in Ezekiel, where it accrues, however, quite distinctive prophetic overtones. Ezekiel is commonly addressed by God as "son of man" in ways that prefigure the stories about Jesus: Ezekiel is the "son of man" who acts out judgment against Jerusalem (Ezek. 4:1-7), who dwells "in the midst of a rebellious house, who have eyes to see, but see not, who have ears to hear, but hear not" (12:2), who propounds riddles and speaks allegories to the house of Israel (17:2), who prophesies to the "spirit" or "breath" which gives life to the dry bones of the whole house of Israel (37:9-14). This may go a long way towards explaining Jesus' predilection for this form of self-reference.2
3. Daniel's "Son of Man" coming with the clouds of heaven
The expression readily invokes Daniel's vision in the night of a figure "like a son of man", who comes with the clouds of heaven to the throne of the Ancient of Days (Dan. 7:14; cf. Matt. 24:30; 26:64; and parallels; Rev. 1:7). I maintain that this vision and its apocalyptic framing in Daniel provide a core prophetic narrative paradigm by which Jesus accounts for the events that are about to impact Israel.
Daniel's figure in human form—this is all that the phrase means here—coming on the clouds of heaven is intended to contrast with the four misshapen beasts that emerge from the sea: human figure associated with the clouds of heaven, horrible beastly figures associated with the chaos of the sea (Dan. 7:3-8). The beasts represent a sequence of destructive earthly kingdoms or empires (7:17-18, 23-26). The human figure represents that part of Israel which remains faithful to the covenant during the crisis provoked by the attempt made by Antiochus Epiphanes—the "little horn" on the head of the fourth beast—to suppress Jewish worship and identity (7:25, 27; cf. 11:29-35). The central point of the vision is that when the beasts are judged, the "son of man" figure will be given kingdom and authority, to the effect that righteous Israel will not only be vindicated for its obedience to YHWH but will come to rule over the nations. This is essentially a political vision regarding the future status of Israel vis-à-vis the surrounding pagan nations.
Jesus deliberately takes this symbolic narrative and reapplies it, not simply to himself—though he is clearly at the centre of it—but to the whole political-religious situation facing first century Israel. He uses it as an interpretive grid in order to make sense of his own role and of the experience of his disciples in the impending crisis of judgment and restoration. The apocalyptic narrative suggests that the outcome will be the destruction of apostate Israel, the vindication of the persecuted churches of believers, and the public or "political" elevation of this righteous people amongst the nations, which will have to acknowledge the sovereignty of Israel's God.
So Jesus as "Son of Man" embodies or represents a community that will suffer in the course of an impending political-religious crisis but will be vindicated and will receive a kingdom which will in some form result in the nations serving the God of Israel. This is the same kingdom that the God of heaven will set up "in the days of those kings", which will "break in pieces all these kingdoms and bring them to an end" (Dan. 2:44). In other words, the coming kingdom of God, which will be given to the Son of Man community, will put an end to the pagan empires that dominated the ancient world from Babylon through to Rome (though Daniel's series presumably culminates in the Greek empire that spawned Antiochus).
At the heart of Jesus' self-reference as "Son of Man", therefore, is the following narrative or argument.
1. First century Israel faces a crisis analogous to the crisis faced by Israel in the second century BC. It is not exactly the same as the earlier crisis—in fact, it is a much more serious one, and much more is at stake.
2. As a "Son of Man" like Ezekiel Jesus bears dramatic, riddling prophetic witness to both the judgment and the restoration of Israel. This seems to me an overlooked but really quite potent aspect of Jesus' self-reference as "Son of Man".
3. Like the community of the "saints of the Most High" (Dan. 7:18-22), Jesus will suffer rather than side with apostate Israel; he will spearhead a faithful alternative; he will embody the ideal of obedient Israel; he will establish a narrow and difficult path leading to the life of the age to come for the people of God.
4. In his death and resurrection, however, he will also anticipate the inevitable experience of the new community of faithful Israel that he has formed around himself. Others have been called to take up their cross and follow the "Son of Man" down the narrow and difficult path leading to life (Matt. 16:24-28). They do so with the assurance that within a generation they will be publicly vindicated for their hazardous trust in this crucified Messiah.
5. The final outcome of this very Jewish apocalyptic narrative—prefigured in Daniel—is that the suffering, persecuted, faithful "saints of the Most High" will receive a kingdom that will break the pagan nations, that will bring an end to pagan empire. As things turned out, this was to be the progressive conversion of Rome following the victory of Constantine over Maxentius. The people of God went on to become a "great mountain and filled the whole earth" (Dan. 2:35). Or to use Jesus' equally political metaphor, a great tree in which the birds of the air build their nests (Matt. 13:32; Mk. 4:32; Lk. 13:19).