This verse is for after Satan and all the remaining fallen angels are sent to the fiery lake. The people alive for the 1,000 years are witnesses to that and then this verse is how they get to Mount Sion from Hebrews:12 as that is where the great white Throne is located. They arrive already perfected so they can enter New Jerusalem as soon as they arrive there.

Isa:51:6:
Lift up your eyes to the heavens,
and look upon the earth beneath:
for the heavens shall vanish away like smoke,
and the earth shall wax old like a garment,
and they that dwell therein shall die in like manner:
but my salvation shall be for ever,
and my righteousness shall not be abolished.

The prophecy below ties in with the creation of 'the time of the Gentiles' from Luke:21:24 as that started in 70AD. Re:11 picks it up when there are 42 months left.

De:4:30:
When thou art in tribulation,
and all these things are come upon thee,
even in the latter days,
if thou turn to the LORD thy God,
and shalt be obedient unto his voice;
De:4:31:
(For the LORD thy God is a merciful God;)
he will not forsake thee,
neither destroy thee,
nor forget the covenant of thy fathers which he sware unto them.

The last woman in Re:12 are the people that are sealed from the effects of the trumps. The 144,000, the two witnesses, and the Church, whose final number is 1/3 of all gentiles that are alive on the day the 7th trump sounds. The 'remnant' being referenced is the two witnesses and them alone as they are the only ones preventing Satan and the Beast from gaining control of Jerusalem.
Jesus doesn't come and save Jerusalem, he comes 3 1/2 days after the celebration of her falling has been going on. God only allows Satan to have the city for 3 1/2 days.