Jude 1:6 And
the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.
Jde 1:6
And angels (ἀγγέλους τε) the
ones not guarding
at some point (τοὺς μὴ τηρήσαντας, aorist active participle) the beginning
state/mandate of themselves (τὴν ἑαυτῶν ἀρχὴν), but instead (ἀλλὰ) lacking away
at some point (ἀπολιπόντας, aorist active participle) the own habitation (τὸ ἴδιον οἰκητήριον), into judgment (εἰς κρίσιν) of a great day (μεγάλης ἡμέρας) in endless chains (δεσμοῖς ἀϊδίοις) under darkness (ὑπὸ ζόφον) he has reserved (τετήρηκεν).
My own paraphrase of the sense of the Greek text.
And those angels, who did not stick to their own original mandate/position as servants of mankind, but instead left behind/lost access to, and are now wanting, their native dwelling-place/glory, God has reserved in unbreakable chains for a great day's judgment, when the saints will judge them.
The word for "left" in "left their own habitation" is a combination of "leipO" (I lack) and a prefix "apo" (away). It occurs six times in the New testament. It is sometimes translated as "to remain", and sometimes as "to leave". I believe the correct concept is "to leave/abandon/forsake something or someone, but realise that you lack/need it now." This meaning fits all its occurrences in the NT.
2 Tim 4:13 Paul left his cloak at Troas but feels a lack of it/wants it now,
2 Tim 4:20 Paul left Trophimus sick at Miletus, but is feeling a need for his assistance now.
Heb 4:6 and 9 it occurs in the present passive form, speaking of the rest of God offered to men that was forsaken, but he is sorely in need of now.
Heb. 10:26 The wilfully sinning once-upon-a-time believer has abandoned the sacrifice for sins, but is sorely in need of it now.
And Jude 1:6 The angels who wanted to rule men rather than serve them, have abandoned the dwelling place they were created for but a sorely missing it now. "Dwelling place" (oikEtErion) is used twice in the Bible: once here and once in 2 Cor. 5:2
2Co 5:2
For in this we groan, earnestly desiring to be clothed upon with our house
G3613 which is from heaven:
In 2 Corinthians it refers to the glorious heavenly body that saints have in heaven while awaiting Christ's return, and which will be overlaid upon our resurrected physical body.
We are told that the chains are temporally endless, not that the incarceration of the angels is temporally endless. That is why I translate it as unbreakable chains. Christ or the saints may be able to unloch the chains with the keys of the kingdom. I don't think the wording implies that the angels can never be released and forgiven. There may be some whose hearts at the judgment are broken and contrite.