The Son of Man 'comes' from the point of view of the heavenly world, that is, he comes from earth to heaven, not the other way around. In other words, his 'coming' in this sense is not his 'return' to earth after a sojourn in heaven, it is his ascension, his vindication, the thing which demonstrates that his suffering has not been in vain. And so, he lists three signs that go to prove he has been vindicated by God: 1. His resurrection and ascension (Effectively reversing the judgment of death and burial he had received from the worldly, human authorities.); 2. The destruction of the temple (Speaking as a prophet, Jesus predicted that it would fall, not as an arbitrary exercise of his prophetic powers, but because it had come to symbolize all that was wrong with the Israel of his day. As well, he had predicted the terrible suffering that would precede it. That's why, in v. 25, he underlines the fact that he has told them about it beforehand. Jesus must be recognized as a true prophet--the Messiah was to be 'a prophet like unto Moses'--and so, when the temple is finally destroyed as he had predicted, that will be a sign that he was speaking the truth. The result will be that his exaltation over the world, and over the temple, will be written in bold letters onto the pages of history; or, as they would put it, "Then the sign of the Son of Man will appear in heaven" [v. 30]); and 3. The news of Jesus' victory will rapidly spread throughout the world. When we hear the word 'gospel' today, we automatically define it in our minds as meaning, "the message of salvation," and there's nothing wrong with that, but this definition should not supercede what the word indicated in the ancient world, where it designated either the military victory of a Roman emperor or the birth of a new emperor. Thus, in this context, the 'gospel' messae that is being spread is the victory of Jesus, that he is God's Messiah, and that he is the true Lord of the world, not Caesar. Or, as they would put it, "He will send out his messengers