The Abyss

The Abyss is mentioned a handful of times in Revelation and outside of this eschatological book in Romans 10:7 and Luke 8:31, the latter verse being where Legion, the multitude of demons that have possessed a man, pleads with Jesus not to cast the spirits into this place.  In its first appearance in Biblical texts before Jesus drives Legion into nearby pigs, it is already associated with demons.  More colloquial uses of the word abyss have come to convey a deep chasm, pit, or sea; the abyssopelagic zone of the oceans (4,000-6,000 meters below the surface) is named in such a way.  Romans 10:7 addresses how no one needs to pull Jesus out of an/the abyss because he has already resurrected.  Of all the uses of the word in the New Testament, this is the least substantial and precise, more like the colloquial usage.  Christian metaphysics refers to something more specific than a general depth or void by this word in the formal sense, which is always elsewhere connected with angelic creatures.

The Abyss is not hell, for it is the default residence of certain demonic beings (Revelation 9:1-6) ahead of the final judgment and is the later temporary holding place for Satan (Revelation 20:1-3) before anyone other than the beast and false prophet have been cast into the lake of fire (Revelation 19:20).  Hell is where sinners are killed by fire for their wrongdoing (2 Peter 2:6) and is only filled near the very end of the Biblical eschatological sequence, while the Abyss is a dimension tied to various rebellious, malevolent angelic entities prior to this.  The latter could not be the place of torment and cosmic execution created to punish the devil and his angels (Matthew 25:41).  Only after Satan is released from the Abyss is he put in hell (Revelation 20:10) to be burned to death (Ezekiel 28:11-19, even if it is not specifically talking about Satan as seems to be the case, clearly presents its demon as being killed rather than tortured forever).

The Abyss is mentioned far earlier in Revelation than the binding of Satan for a millennium, though.  For the fifth trumpet judgment, a star falls to the planet that opens the Abyss.  Smoke comes out of it as if from a great furnace to the point of obscuring the sun (9:2), along with locusts that possess human-like faces and hair, teeth like a lion's, armor, clamorous wings, and stinging tails like a scorpion's (9:3-10).  Presiding over these locusts is the Destroyer, the angel of the Abyss (9:11).  The only other thing mentioned about this figure is that its name is Abaddon in Hebrew and Apollyon in Greek.  This information only tells us its name as opposed to its allegiances, intentions, and so on, but nowhere else is this presence referenced in the Bible.  However, its subordinate "locusts" are eventually given the power to torment people for five months as death is kept from all their victims during this time.

Revelation 11:7 and 17:8 both refer to a beast that comes up from the Abyss.  Chapter 13's beast that comes out of the sea to demand worship, controlling all economic transactions by mandating a mark of allegiance to it and/or the dragon, is likely that beast.  In Revelation 13:3, there is a statement about how the beast has a head with a fatal wound that is healed, inspiring many to marvel and submit to this being.  Verse 8 of chapter 17 says the beast was, is not, and will come up out of the Abyss, an almost certain reference to the same beast from the sea (might I add, it rises to be destroyed, the verse says, not to be tortured forever).  Whether this beast originates from the Abyss to start with or is possessed by a demon after some sort of resurrection, there is something about this ruler that is demonic in its power.  The beast, like Satan, is doomed to perish in the lake of fire (Revelation 19:20 once again) instead of being left in a chasm-like prison.

Mentioned more often than Tartarus (2 Peter 2:4) but far less than Sheol and the lake of fire, the Abyss is not presented as a place of torment, but as one of captivity for a time.  It is no demon's permanent dwelling and not all demons are inside.  If this was not so, Legion would not have entered a person's body and would be in the Abyss instead of asking to not be banished there.  Also, Satan would not have to be placed inside if all demons were already there.  The end of these beings arrives in the second death of the lake of fire, though for demons thrown in without death and resurrection beforehand, hell is not an afterlife.  It is just a final destination.  Since eternal life is derived from God or his blessing (Romans 6:23, 1 Timothy 6:16) and his enemies are to die (Ezekiel 18:4, 1 Corinthians 15:26, and see 2 Thessalonians 1:3-8 on the seeming eschatological antichrist being killed in hell at the Second Coming), they will not forever reside in Gehenna either.