God speaks of a number of times that Israel is dispersed and then regathered back together. Over and over again, Israel would abandon their belief in God and sin, be judged, and then finally learn their lesson and be returned to the land. One mistake we make when we read about these times though, is thinking that every single person had repented and turned back to God. When we think logically however, that of course simply isn't true. God has always kept a remnant of people who were true believers, but the vast majority were usually very superficial in their belief and would turn at the slightest provocation, and some never believed at all. Another thing to keep in mind is that God's remnant has always been "small". It's never been a large group of people, such as an entire nation.
Obviously, the last time they were dispersed came as God's judgement on them for rejecting His Son, which was carried out in 70ad by the Romans. this time, they were ultimately dispersed all over the world instead of to just one specific place. According to God's prophetic clock, their regathering would begin in the end times with the vast majority still being unbelieving and dead spiritually.
It must be this way, if God's Word is true. For the main purpose of the tribulation is to bring Israel, the Jew's, to recognize Christ as their Savior. If they already believed, the tribulation wouldn't be needed. I realize that the way I've worded this, makes it sound like God is being mean to them and forcing them not to believe so He can punish them, and that's not at all true! It's just hard for me to explain it in the right way, so please don't think that for even a second! The Tribulation, which is also called "the time of Jacob's trouble" is a time specifically for the Jew's to be purified and their hearts turned back to the Lord, once and for all time. God has planned to do this so that He can save a remnant of His people Israel so He can fulfill all the promises He made to them.
Zephaniah 2:1–2 —Gather together, gather together, O shameful nation, *before the appointed time arrives and that day sweeps on like chaff, before the fierce anger of the Lord comes upon you, before the day of the Lord’s wrath comes upon you. *
Zechariah 13:8–9 —In the whole land,” declares the Lord, “two-thirds will be struck down and perish; yet one-third will be left in it. *This third I will bring into the fire; I will refine them like silver and test them like gold. They will call on my name and I will answer them; I will say, ‘They are my people,’ and they will say, ‘The Lord is our God.’ ” *
I often have found myself looking down on the Jew's as I read the OT, and thinking how horrid they were for turning from God, over and over again. I've thought that they acted stupidly, and even illogically at times. Yet, when I'm honest with myself, with the help of the Holy Spirit, I realize that I'm just exactly like they were and are. I too have turned away from Him, acted and thought stupidly and illogically at times. etc. They really haven't done anything that I haven't also done. Really, all the OT is just a picture of each one of us and like the Lord tells us, it was written and given to us to teach us. 1 Corinthians 10:6 —Now these things occurred as examples to keep us from setting our hearts on evil things as they did. * and verse 11 tells us they're warnings to us as well.
Right now, the eyes of the Jew's have been blinded so that we could be saved. (Romans 11:7–8) God didn't just decree that they'd be blind because He wanted it that way. They chose that path and had been walking on it for a very long time. Lest we forget though, we also chose that very same path, so we are no better then they were or are.
In Romans 11, Paul does a great job of explaining it and reminding us that even then (and now also) there is a remnant of Israel that was chosen by God, by His grace. (Romans 11:5) They don't deserve it anymore then we deserved our salvation, but God has chosen some to receive His grace. Paul states quite clearly in Romans 11 that the Jew's will eventually be saved, and this will occur due to the tribulation: Romans 11:25–27 —I do not want you to be ignorant of this mystery, brothers, so that you may not be conceited: Israel has experienced a hardening in part until the full number of the Gentiles has come in. *And so all Israel will be saved, as it is written: “The deliverer will come from Zion; he will turn godlessness away from Jacob. *And this is my covenant with them when I take away their sins.” *
When the "full number of the Gentiles has come in", the rapture will occur and the world will then begin to see the wrath of God against all ungodliness. You see, the Church has no purpose on the earth any longer once the last Gentile as been saved. The Church is kind of like a parenthesis in the history of Israel. I say that because God chose the Jew's out of all the other people, and He spent all those centuries preparing them to be His priests. They fumbled the job as He knew they would, so He basically stopped His prophetic clock so the Church could be born and the Gentiles saved. Once that's done, He will again start His prophetic clock again and the Jew's once again will be the center of His attention. (you can find this starting in Daniel 9:20)
Some people say that the Church could have the purpose of witnessing, but again, if God's Word is true, and I believe it is, we can see that the Church itself is falling apart at the seams, and is already a horrible witness. What makes us think that we'd do any better during the tribulation? Are we really that conceited? Besides which, as far as the church is concerned, God tells us that it will continue to go downhill during the end times, until finally it gets to a point where there are very few people left that are really saved and living their lives for Christ. You see, despite our tendency to think we're better then the Israelites were in the OT days, we've done the very same thing they did. It just proves God right yet again, that we humans cannot save ourselves and are totally incapable of doing right.
So the bible teaches that the Jew's will be regathered to Israel as unbelievers. At some point soon, most likely after the rapture, the Jew's will build another Temple. The Tribulation officially starts when the Antichrist signs a 7 year treaty giving them 7 years of protection, which of course he has no intention of keeping. But let's look closely at what we're told in Daniel because this tells us yet again the purpose of the Tribulation: Daniel 9:24 —“Seventy ‘sevens’ are decreed for your people and your holy city to finish transgression, to put an end to sin, to atone for wickedness, to bring in everlasting righteousness, to seal up vision and prophecy and to anoint the most holy. *
Do you see it?
1. finish transgression (restrain sin, speaking particularly of Israel’s in their long time of apostasy.)
2. to put an end to sin. (to judge it with finality;)
3. to atone for wickedness. (the eyes of the Jew's will be opened and they'll accept Jesus as their Savior and His work on the cross will atone for their sins, just as they did ours)
4. to bring in everlasting righteousness. (they'll be given a new nature as we were but their complete change will be more instantaneous then ours was.)
5. to seal up vision and prophecy (prophecy is "unsealed" until it is fulfilled, so this is saying that God will fulfill all His promises to them at this point)
6. to anoint the most holy. (there are two views of this one, and both may be correct. One is that this is talking about the anointing of the New Temple for the Millennium and the other is that it's talking about the anointing of Christ as ruler over the earth during the Millennium. Both make sense.)
Let me add something from a commentary about the phrase, "to bring in everlasting righteousness." that you may find interesting: The word “everlasting” (here pl. in Heb.) means ages. Thus this phrase (lit., “to bring in righteousness of ages”) is a prophecy that God will establish an age characterized by righteousness. This is a reference to the Millennial kingdom (Isaiah 60:21 —Then will all your people be righteous and they will possess the land forever. They are the shoot I have planted, the work of my hands, for the display of my splendor. *; Jeremiah 23:5–6 —“The days are coming,” declares the LORD, “when I will raise up to David a righteous Branch, a King who will reign wisely and do what is just and right in the land. *In his days Judah will be saved and Israel will live in safety. This is the name by which he will be called: The LORD Our Righteousness. *). The Bible Knowledge Commentary
So you see, this is all about Israel and everything is God's doing. Just as we couldn't save ourselves and were and are helpless to help ourselves, so are they. At the second coming, the Lord will graciously forgive all their sins, give them a new nature like He did us, and usher in what we call the Millennial Kingdom in order to keep all the promises He made to the Jew's in the Old Testament.
It's really a wonderful, awesome picture that shows us that no matter how unfaithful we are, our God is faithful to us to keep His promises. We cannot save ourselves, nor can we keep ourselves saved. (It boggles my mind that some people are determined to think that they have the power to do that!) Praise God that He can and will save us and promises to keep us saved to the very end! It's just like He tells us in 2 Timothy 2:13 —if we are faithless, he will remain faithful, for he cannot disown himself. *
One last point I'd like to make about Israel being unbelieving like they are now is another place in God's Word this is shown very clearly. It's the prophecy of the dry bones in Ezekiel 37. If you read verses 4-8, you see that everything comes together, but there's a problem...there's no breath in them. As I'm sure you're aware, breath is a symbol for God's Spirit which we receive at salvation. It isn't until verse 10 that we see the breath enter the bones and they live. Until then, they're dead spiritually. In fact, if you read this prophecy carefully you'll see there are stages to their "rebirth". (can't think of another word for it) They are simply dead dry bones to start with, then they go through several stages before finally having breath given them. This makes it quite clear that Israel would enter their land again as unbelievers, spiritually dead, only to be given the breath of spiritual life and health by God at the second coming. It shows yet again that it's all God's doing, all because of His love, mercy and grace and not because of anything they do or did. It's the same way with us too. What an awesome God we serve!
I never did finish telling you the rest of the purpose of the tribulation! God isn't ignoring the Gentiles. Part of the reason for it is also to judge and punish the nations for their sins, most especially for the way they've treated Israel over the centuries. It's a vivid demonstration of the horrible consequences of sin. Because our sins have already been judged, there is no reason for the church to be on the earth during the tribulation, and of course, the Lord promises us that we won't be! Praise God!!!! 
It won't matter if they want to go or not (although I can't imagine anyone not wanting to!) There will be no warning, no discussion, no questions and answers, just a command; and we will obey because our bodies will have no choice in the matter.