I've dealt with this before, but I want to visit it again. I believe I'm getting a better picture now. Jesus was addressing *Israel* specifically. He was still under the era of Law during his earthly ministry. So Israel was in sight, and not the outreach to the Gentiles just yet.
So Jesus described the future of Israel in the NT period. They would reject him as their Messiah--all but a relative narrow band of followers, who later would be called "Christians." Israel, among the majority, would continue in sin, even while they were still under the covenant of Law. They would perform in a religious sense externally, but not inwardly. They would perform the works of the Law, but not produce true spirituality.
And thus, Jesus predicted that their whole system of worship would come down. The temple--the center of their worship, and the center of the Law--would come down. The covenant would be smashed. This didn't mean, however, that Christ was rejecting Israel for all time. It only meant that he was rejecting those who were rejecting him. Those who would accept him would be saved.
And so, the Olivet Discourse includes both unbelievers and believers in Israel. So when he talked about the coming of the Son of Man--his own coming with his Kingdom, he talked about final judgment against both Israel and the enemies of Israel among the nations. And he talked about the salvation not just of Christians in Israel but also of Christians who would later emerge from other nations.
But as I said, this Discourse was at that time largely focused on Israel. It did, necessarily, include the Christians in Israel because 1) Jesus was talking to his own disciples, and 2) any discussion of Israel would have to include the faithful in Israel.
So Jesus' coming as the "Son of Man" depicted the coming of his Kingdom, as we can see in Daniel 7. The coming of the Son of Man is directly associated with the coming of the Messianic Kingdom. And that in turn is directly associated by the Prophets with the salvation of national Israel from hostile nations--a time when Israel shall never be destroyed again.
So how did Jesus explain the end of sin in Israel to allow this final salvation of Israel? In his own generation a judgment would begin against Israel--the judgment of 70 AD. And this would constitute a "time of great distress" for the Jews throughout the NT age, up and including the end of the age. The wicked in Israel would be destroyed. The sinners in Israel would be continuously judged until the time came when final destruction would be brought about at the coming of the Son of Man.
But this coming to save Israel from the hostile nations necessarily included a faithful remnant of Christians in Israel. This was a word for *all Israel* in NT history, and had to include Christians among the Jews. What Jesus was basically saying is that the wicked in Israel would be judged, making room for a remnant of Jews who would convert, like the Christians, to Christianity. And this would bring about the salvation of the entire nation at his coming.
So where does the Rapture of the Church fit into this scenario? Inasmuch as this Discourse is largely directed at Israel it seems to exclude the Gentile Church. But it really doesn't. It's just pre-Christian. Later, Jesus would give his Great Commission, and that would automatically include Gentile Christians in the promise God made regarding Israel. If Israel's Christians would be saved, enabling the nation to be saved, then Christians in other lands would also be saved, enabling their own nations to be saved!
Thus, the gathering of "God's elect" is for Jesus a reference to both the honoring of the Christian remnant as well as a reference to the salvation of the nation they represent. I think we divide the Rapture of the Church up from its intended target, which is the restoration of the nations to God at the coming of Christ.
This Discourse seems to address the need for God to save entire nations, and does not deal in particular with what happens to the Christian remnants of nations in the world. I think Acts 1 may come closer to describing how Jesus comes back specifically for Christians. But I'm still researching this. Let me know what you think?