Another thing people don’t think about is how “every eye” that is supposed to be able to see Him coming physically can do so without a flat earth and some extraordinary high-powered telescopes. The “broadcast live on television” argument doesn’t cut it, since plenty of homes the world over are still, and will be for quite some time, without televisions.

Again, I just can’t see how one can dichotomize the “coming on the clouds” language and the cosmic signs language. We’ve got to be better-versed in the literature of the Old Testament when we read the New Testament.

1) “The first part” you mention actually extends through verse 28. This is all instruction (don’t be alarmed, flee, don’t believe false prophets, etc.), aimed, as you suggested, at Jesus’ immediate audience, the disciples. They had just asked for the sign of His coming, and He was answering their question.

2) Then in verse 29, as even the NIV’s footnotes point out, Jesus basically starts re-capitulating Isaiah’s imagery from Isa 13:10 and 34:4. Having divulged the signs of His coming that, incidentally, definitely occurred in the disciples’ lifetime, and having given instructions on how to abide this time, He then goes on to describe the meaning and significance of the events He’s been predicting by situating it in the familiar language of the prophets. He returns to instruction, this time parabolic, in verse 32 and again in 42ff through chapter 25. Jesus is using a wide range of genre here.

3) I do not mean to suggest that there were no observable, physical events surrounding the Second Coming. Clearly, the Roman siege (which lasted close to four years) was observable. What was not observable was what was going on behind those physical events, i.e. in the realm of the spirit. Plenty of modern students of history read about the destruction of Jerusalem under Titus and “observe” it, but they don’t know what God was accomplishing through those physical events. Apocalyptic imagery is revelatory: it reveals what’s going on behind the veil of the physical and observable. Thus these physical events with spiritual significance transpired in the very same way that God’s holding the right hand of Cyrus (Isa 45:1) was observable insofar as God’s will was accomplished through Cyrus’ conquests.

“For the stars of heaven and their constellations will not flash forth their light. The sun will be dark when it rises, and the moon will not shed its light.”

Similarly, Isaiah 19:1 has God coming on a cloud in judgment of Egypt. No historical records of that, either. Ezekiel 32, Amos 8, etc. use the same sort of apocalyptic language that Jesus used, yet we have been conditioned to view Jesus’ diction in isolation from that of the Old Testament.

In short, you are taking the language of the Olivet Discourse as a prophecy of literal, observable events. Yet look at what Jesus said in Luke 17:20-25:
“The coming of the kingdom of God cannot be observed, and no one will announce, ‘Look, here it is,’ or, ‘There it is.’ For behold, the kingdom of God is among you.” Then he said to his disciples, “The days will come when you will long to see one of the days of the Son of Man, but you will not see it. There will be those who will say to you, ‘Look, there he is,’ (or) ‘Look, here he is.’ Do not go off, do not run in pursuit. For just as lightning flashes and lights up the sky from one side to the other, so will the Son of Man be (in his day). But first he must suffer greatly and be rejected by this generation.”

Some latch on to the “lightning” imagery and say, “See! It’s an observable event!” Rather I think He’s saying that His coming would not be geographically bound to one single location as a literal “coming on the clouds” demands, but that the effects of the Kingdom would be worldwide in effect (think of how lightning starts in one spot and flashes around the whole sky). But whatever the meaning you take from this imagery, remember that Jesus seemed to think that this imagery did not contradict His claim a few verses before that the establishment of the Kingdom would not be observable.