Christ both stood on the Mount of Olives to begin with on AD 70’s Pentecost day, and then gathered His resurrected saints to meet Him in the air as He brought them with Him back to the Father in heaven. This is not a contradiction of two activities as you assume. It’s what Christ promised the disciples He would do for them; “And if I go, I will come again and RECEIVE YOU UNTO MYSELF, that where I am, there ye may be also.” This is a scenario that does NOT include Christ remaining on this planet on that particular occasion, as will likely occur later at the close of human history.
The eastern gate of the temple was the portal through which the resurrected saints left the city to join Christ in the air as they all left this earth together back then in AD 70. Remember that eastern gate of Zerubbabel’s rebuilt temple court in Ezekiel 46:1-3? The people were to worship facing that eastern gate in the sabbaths and the new moons back in those days. It was a gate by which only the high priest “prince” could enter and leave the temple courts, and was to remain shut except for the sabbath day of the week and on the day of the new moon.
This worship of the people facing this eastern gate was to symbolize the location - and the timing - of the Messiah’s return to gather His resurrected saints through that eastern gate. Since this particular temple with its eastern gate was destroyed in AD 70, that shows us that the fulfillment of the purpose for that eastern gate at Christ’s return took place JUST BEFORE that eastern gate was destroyed along with the Temple in AD 70. What we now live in is the New Jerusalem in this New Covenant Age, whose gates are NEVER SHUT (Rev. 21:25).
You have said that the only return Christ mentioned was to take place after the “Great Tribulation” and that you think that unequaled tribulation period hasn’t happened yet. This also is a flat contradiction of some very plain verses.
Apparently you think the “days of vengeance” and the “Great Tribulation” are totally different periods. Not so. According to Luke 21:22-23, they are exactly the same thing. “For these be the DAYS OF VENGEANCE, that all things which are written may be fulfilled. But woe unto them that are with child, and to them that give suck in those days!” (those days of vengeance) “for there shall be *GREAT DISTRESS* (great tribulation) IN THE LAND, and wrath upon THIS people.” (meaning “THIS GENERATION” living in Christ’s days that wouldn’t pass away until all those “days of vengeance”/ “great distress / tribulation” had passed (Luke 21:32).
And that’s “DAYS”, by the way - not almost two MILLENNIA of vengeance and judgment until Hitler’s holocaust. The blood curse the high priests called down upon themselves was upon the families of a SINGLE generation that killed the Messiah in AD 33 - not every person since AD 70 who has ever followed Judaism.
And the Zechariah 14:4-5 LXX verses never predicted a split of the Mount of Olives that would create a valley. That Zech. 14:4-5 LXX text said the Kidron Valley would be “BLOCKED UP” as far as Azal, which is just south of the city of Jerusalem. That means the Kidron Valley was filled in with rubble from the earthquake that shook the mountain and broke it into rubble that slid down the mountain, just like it did in King Uzziah’s days. A genuine earthquake in King Uzziah’s days was going to be duplicated IN THE SAME MANNER at Christ’s AD 70 coming. Which it did, and which has been documented and analyzed by archaeologists, even though you still are turning a blind eye to the physical evidence.