Consider the text of Isaiah 26 is filled with talk of the First Resurrection, which had not yet happened when this text was written. My notes are in red.
1 In that day this song will be sung in the land of Judah:
“We have a strong city;
he sets up salvation
as walls and bulwarks.
2 Open the gates,
that the righteous nation that keeps faith may enter in.
[Note: I think that this is a reference to the First Resurrection of Revelation 20, which happened in Matthew 27:51-53. That is, that “the righteous nation” did indeed “enter in” to the Holy Land that day, their spirits having been freed through the “gates” of Sheol, such that they could reinhabit their reconstituted natural bodies.
3 You keep him in perfect peace
whose mind is stayed on you,
because he trusts in you.
This is a reference to those who had been in the “Paradise” section of Sheol up until that First Resurrection.
4 Trust in the Lord forever,
for the Lord God is an everlasting rock.
5 For he has humbled
the inhabitants of the height,
the lofty city.
He lays it low, lays it low to the ground,
casts it to the dust.
6 The foot tramples it,
the feet of the poor,
the steps of the needy.”
I suspect that this is a reference to the casting down of Satan and his order of angels from heaven to earth.
7 The path of the righteous is level;
you make level the way of the righteous.
8 In the path of your judgments,
O Lord, we wait for you;
That is, we righteous who are in Sheol
your name and remembrance
are the desire of our soul.
9 My soul yearns for you in the night;
my spirit within me earnestly seeks you.
For when your judgments are in the earth,
the inhabitants of the world learn righteousness.
10 If favor is shown to the wicked,
he does not learn righteousness;
in the land of uprightness he deals corruptly
and does not see the majesty of the Lord.
11 O Lord, your hand is lifted up,
but they do not see it.
Let them see your zeal for your people, and be ashamed.
Let the fire for your adversaries consume them.
This, I believe, is that “eternal fire, prepared for the devil and his angels.” That is, the “Lake of Fire”. The righteous captives in Sheol are waiting for God to punish Satan for his wrongs.
12 O Lord, you will ordain peace for us,
for you have indeed done for us all our works.
13 O Lord our God,
other lords besides you have ruled over us,
This is likely a reference either to the Watchers who intermarried with human women (See Genesis 6 and 1 Enoch 6), and who were imprisoned for it until the great judgment, or to the unfaithful angelic “shepherds” that God put over Israel for a time. See their destruction in vs. 14 below.
but your name alone we bring to remembrance.
14 They are dead, they will not live;
they are shades, they will not arise;
to that end you have visited them with destruction
and wiped out all remembrance of them.
15 But you have increased the nation, O Lord,
you have increased the nation; you are glorified;
you have enlarged all the borders of the land.
16 O Lord, in distress they sought you;
they poured out a whispered prayer
when your discipline was upon them.
The incarcerated Watchers pleaded with Enoch to ask God to release them. (God said no.)
17 Like a pregnant woman
who writhes and cries out in her pangs
when she is near to giving birth,
so were we because of you, O Lord;
18 we were pregnant, we writhed,
but we have given birth to wind.
Yet they would be brought forth by God in that First Resurrection, as foretold here:
We have accomplished no deliverance in the earth,
and the inhabitants of the world have not fallen.
that is, the fallen elohim were still generally in business.
19 Your dead shall live; their bodies shall rise.
You who dwell in the dust, awake and sing for joy!
For your dew is a dew of light,
and the earth will give birth to the dead.
this is the First Ressurection
20 Come, my people, enter your chambers,
and shut your doors behind you;
hide yourselves for a little while
until the fury has passed by.
Having foretold the resurrection that they should expect, God now comforts his dead, telling them to take shelter in the Paradise of Sheol.
21 For behold, the Lord is coming out from his place
to punish the inhabitants of the earth for their iniquity,
and the earth will disclose the blood shed on it,
and will no more cover its slain.
The “inhabitants of the earth” is the same as “those who dwell on the earth” in other passages. It’s a reference to the rebel elohim. This passage also brings to mind “the blood of Abel” and that fourth area of Sheol that was for those who protested their deaths, as did Abel. And further, here, we see that a time would come when the earth would no long “cover its slain”. This, I believe, is another way of describing their resurrection from Sheol.