Read Zechariah 13-14 at Bible Gateway.
The prophecy that idolatry will be cut off (Zec 13:1-6) has been fulfilled. When Judah came back from Babylonian captivity, they served the LORD all through Persian rule. The Greeks under Alexander the Great overcame the Persian empire, and under the rule of the Greeks, a cosmopolitan worldliness was introduced into Judean culture. Some of the Jews embraced Greek culture, even where it expressly went against Hebrew culture established by Torah.
This test of the Greeks is part of the process of refining His people like silver is refined, and testing His people as gold is tested (Zec 13:9). Refining and testing do not take place where there is no opposition, no trials, no persecution. You have to be challenged to see whether you will in fact remain loyal to the LORD God in the face of a challenge.
The Jews were tested throughout Greek rule, and Roman rule, and even Christendom’s rule, and because of these tests, idolatry among them has been cut off.
The prophecy of the shepherd has been fulfilled (Zec 13:7-9). Yeshua in His first coming is the Shepherd who was struck (arrested, tried, and crucified) so that the sheep would be scattered (His disciples ran from Him so that He was alone in His ultimate test).
The prophecy of the Day of the LORD has yet to be fulfilled (Zec 14). We have seen already that all the nations will come against Jerusalem, and the LORD will ultimately deliver her. In Zec 14, we learn that the city will be divided (the city will be taken, so that half of the city will go into captivity). The nations, most likely in the form of the UN, will succeed in dividing the capital by force of arms. The discussion of dividing Jerusalem is in the news in our day, so it is very likely that we will see this fulfillment in our lifetimes.
But it is this act of violence against His people and His city that will bring about the LORD’s return. He will descend bodily, Messiah Yeshua, until His feet touch down on the Mount of Olives. That Messiah Yeshua is YHVH incarnate, the Hebrew Scriptures preach, for this is how Yehovah our Elohiym, Creator of heaven and earth, will come. His saints will come with Him (Zec 14:5), who will form a great army, and they will fight against the nations until they have been subdued.
It will not take long: that is the Day (24 hours) of the LORD’s wrath that will be poured out on the nations. Those plagues and that wrath, will bring down Mystery Babylon the Great, and the kingdoms of this world will end, having become the kingdoms of our LORD and of His Christ, and He shall reign forever and ever (we will read Revelation in December). And the LORD shall be King over all the earth (Zec 14:9) — King Yeshua will reign over the nations with a rod of iron (Rev 19:15) for one thousand years, the seventh millennia of rest (Rev 20:4-6). When He is King, there will be no war, nor injustice, and peace will reign (Isa 2:4). The will be the earth’s Sabbath, after six millennia of bondage to sin.
The saints who will return with Him:
But I do not want you to be ignorant, brethren, concerning those who have fallen asleep, lest you sorrow as others who have no hope. For if we believe that Jesus died and rose again, even so God will bring with Him those who sleep in Jesus. For this we say to you by the word of the Lord, that we who are alive and remain until the coming of the Lord will by no means precede those who are asleep. For the Lord Himself will descend from heaven with a shout, with the voice of an archangel, and with the trumpet of God. And the dead in Christ will rise first. Then we who are alive and remain shall be caught up together with them in the clouds to meet the Lord in the air. And thus we shall always be with the Lord. Therefore comfort one another with these words. 1 The 4:13-18
All who are His will return with Him, those who died before His return. Those who are His who are alive at His coming will join with them, and they will live and reign with Him during the Millennial Kingdom (Rev 20:4-6). They will have received spiritual bodies as the Lord Jesus received a spiritual body after His resurrection, so they will not be subject to disease or death. They will be a great many people, who will most likely serve Him as teachers, priests, prophets, and rulers of cities, provinces, and nations during His reign.
Those who were not His at His coming, regular people, will continue their lives under His benevolent reign. They will live, marry, have children, grow old, and die, and so on, for the course of the Millennium. After death, they will sleep with the others who were not His, to await the final resurrection before the Great White Throne of Judgment at the end of the age.
That is my understanding, to this day.