When Jesus predicted the eschaton and the coming of the “Son of Man,” he was probably talking about someone else. I grant that Mark’s Gospel portrays Jesus as the “Son of Man.” But that was probably the conclusion of the church after Jesus died and after several early church leaders had non-veridical visions of him afterward. The reason I think this is because I do not think Jesus arose from the dead, but that takes us away from the topic at hand.
Just look closely at what Jesus said in Mark 8:38 as one example of a “Son of Man” saying: “For whoever is ashamed of me and of my words in this adulterous and sinful generation, of him will the Son of man also be ashamed, when he comes in the glory of his Father with the holy angels.” Bart D. Ehrman argues that when we look at what Jesus actually said about the Son of Man, “there is no indication that he is talking about himself. In fact, if you didn’t know in advance the Christian idea that Jesus was the Son of Man, there’d be no way you would infer it from this saying. On the contrary, just taking the saying on its own terms, Jesus appears to be referring to someone else. To paraphrase the saying: ‘whoever doesn’t pay attention to what I’m saying will be in big trouble when the Son of Man arrives.’”
The “Son of Man” never came as predicted in the lifetime of Jesus. But with the visions the early church leaders had they concluded Jesus was the “Son of Man,” and that he was going to return and set up his kingdom on earth. That too never happened as the New Testament writers thought, for it was to take place as Jesus predicted, in their generation.
This interpretation explains the fact that the eschatological “kingdom of God” talk and the imminent prediction was successively watered down (from Mark to Matthew to Luke), to the point where such talk of an imminent eschaton is completely removed in John’s gospel, and where it replaced the language about “the kingdom of God” with non-eschatological “eternal life” language. In the second-century pseudonymous epistle of 2 Peter 3:3-10, scoffers were already questioning why Jesus didn’t return. There we read: “With the Lord a day is like a thousand years, and a thousand years are like a day.” This comes across as an excuse for why the eschaton didn’t occur in the very generation Jesus said it would.