According to all three accounts of the Olivet Discourse, the coming of the Son of Man will be unmistakable. If something is the sort of thing that could leave one speculating, “I wonder if that was it?” whatever it was, it isn’t the it we were looking for. So many groups (e.g. the Moonies, JW’s, Branch Davidians, among others) could have been spared much of their folly if they’d only taken this word to heart. Nothing about Jesus' actual return will be subtle, and it will not leave intact the course of ordinary living that had been the norm up to the time of its occurrence.
Matthew describes this lack of subtlety as having the quality of lightning flashing across the whole sky. The point is emphasized and clarified by the reference to vultures gathered at a corpse. The point is that when the sign has fully occurred (i.e. the Great Tribulation, which is akin to the corpse) that Christ's return is there on the spot like the vultures gathered in the metaphor. So, there is nothing doubtful about whether or not it will occur, or when the time comes, that is has occurred, anywhere here on earth.
Matthew tells us that Christ's return will happen "immediately" (Koine: eutheos, at once) after the distress of those days, that is the Great Tribulation. The sense of urgency entailed cannot be overlooked, so the return of Christ will come on the heels of the Tribulation without any protracted delay. I envision this as happening right after the outpouring of the seventh bowl at the end of the 70 Weeks. In other words, the seventh bowl of wrath serves as the last bit of the Great Tribulation and ushers in the return of Christ.
All three accounts reference astonishing astronomical events in conjunction with the powers in the heavens being shaken. Luke does not mention them in sequential terms (i.e, as following the Great Tribulation as do Matthew and Mark), but his generality cannot be seen to dismiss the specificity of the other two. Matthew, uniquely, refers to the sign of the Son of Man appearing in the heavens before his coming in the clouds. That sign is never described by Matthew, never mentioned by Mark or Luke, so suffice it to say, it's something we don't need to understand in any depth to know that Jesus is coming back in the clouds (and in the same fashion as he ascended).
Furthermore, we are told that the tribes of earth will mourn at the sign, whatever it might be. Mourn, in this instance, means to bereave the loss or cutting off of something or someone. This is not regret or repentance, this is the agony of defeat (see 2 Thessalonians 2:9-12). At this sign, the Gentiles (tribes) alive at that time finally recognize that they are cut off—that they backed the wrong horse and face nothing but judgment ahead. The blinders come off, the delusion dissipates, and they will see, finally, the truth about Christ with their own eyes, but without faith.
It is infinitely better to see that truth, now, by faith but without sight.
It is infinitely better to see that truth, now, by faith but without sight.
