8 And [kai] the temple [naos] was filled [gemizo] with
smoke [kapnos] from [ek] the glory [doxa] of God, [theos] and [kai] from [ek] his [autos] power; [dunamis] and [kai] no man [oudeis] was able [dunamai] to enter
[eiserchomai] into [eis] the temple, [naos] till [achri] the seven [hepta] plagues [plege] of the seven [hepta] angels
[aggelos] were fulfilled. [teleo] KJV-Interlinear
8 And the
temple was filled with smoke from the glory of God and from His power; and no
one was able to enter the temple until the seven plagues of the seven angels
were finished. NASB
There is always a quiet before the storm. There is always grace before judgment. There is always opportunity to repent and change ones ways, before God lowers the boom.
And during the initial portions of the Tribulation, as in any time in history, God gives truth, doctrine , and opportunity to everyone, so that they can change their ways.
And unlike in history, during this last phase of the Tribulation, God will have squeezed as in a wine press, every person who will ever believe in Christ and be saved, and all that will remain, will be unbelievers who will refuse, stubbornly refuse to believe in Christ even through the most horrifying judgments that anyone will ever face.
Smoke has been used in the past as symbolism to represent the presence of God in all of His glory. When the smoke filled the temple, then no one could enter, Ex 19:16-18, Ex 40:34-35; 1 Kings 8:10-11; Isa 6:1-4.
And so it is here, in our current verse. There will come a time in the Tribulation, near its end, that all who will believe in Christ, will have done so, and no else in that era, will believe.
This will occur only three times in history. The first was during the Noah Flood, when everyone had the chance to believe, but did not, and only eight people boarded the Ark - Noah and his three sons, and each of their respective wives.
The next time in history will be at a time immediately prior to the Rapture, when the 'great' apostasy predicted by Jesus and Paul, will occur at the end of our present dispensation. It will be then that God will shift the gears of history into the next set, removing believers, and leaving unbelievers only, so as to get many more to believe, who probably would not have done so if the Rapture had, or does not occur.
And then at the end of the Tribulation, God will close the temple, so to speak, preventing anyone else from entering. This is not a closed door termination of salvation but a picture showing us that there won't be anyone else who will believe. God will have retrieved everyone who will believe, and there won't be any more.
Such will be the stubbornness of evil in the minds of those remaining alive.
Note quickly, this does not mean that all believers will be in heaven, for there will still be a population of believers on earth, either in hiding or wherever, who will survive all of these judgments against unbelievers, and who will enter into the Millennium after the Second Advent of Christ.