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.
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”.