“For if God spared not the angels that sinned, but cast them down to hell, and delivered them into chains of darkness, to be reserved unto judgment” 2 Peter 2:4
There was war in Heaven (Revelation 12:7) which revealed the character of some of the angles that what would become fallen angels or demons, these were so evil that God would not allow them to walk the earth among men because they were so evil. This war took place before God put man on the earth, Satan was in the Garden as a serpent, which informs us that he was already fallen and judged by God (Genesis 3:1-15, Ezekiel 28:13-19). The demons who are among us now, including Satan, were not as evil as those in the pit which is the distinction between the demons in the pit and those among us today. It is not revealed in the biblical text, whether these demons in the pit will ever be released during the tribulation.
“The Bottomless pit” is one word in the Greek of the New Testament and is literally the “abyss,” which means “bottomless, unbounded, the pit, or the immeasurable depth.” Roman mythology featured a similar place called Orcus, a very deep gulf or chasm in the lowest parts of the earth used as the common receptacle of the dead and, especially, as the abode of demons. The bottomless pit of Revelation 9:1-12 holds a unique type of demon. It is also the home of the beast who makes war against the two witnesses (Revelation 11:7-8). At the beginning of the millennial kingdom, the bottomless pit is the place where Satan is bound (Revelation 20:1-3). At the end of the thousand years, Satan is released and promptly leads an unsuccessful revolt against God (Revelation 20:7-10).
The bottomless pit may be associated with a place called Tartarus. This Greek word is translated as “hell” and is used only once in Scripture, in 2 Peter 2:4. It refers to the place where “angels who sinned” are reserved in chains of darkness for judgment. The NIV says these angels in Tartarus are held in “gloomy dungeons.” These same angels are also mentioned in Jude 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.” Genesis 6:2
If Tartarus is the same as the Abyss, then the inhabitants of the bottomless pit are the same angels who sinned and left their first habitation witch would be Heaven. God uses the bottomless pit as a holding place for the most evil of angels, including Satan himself during the 1000 year reign (Revelation 20:1–3) and those who tried and failed before the Flood to thwart God’s plan to bring the Seed of the woman into the world (Genesis 3:15). The inhabitants of the Abyss are released for a very short time during the last three and a half years of the tribulation to fulfill God’s purpose, namely, to torment the wicked (Revelation 9:5). These prisoners of the bottomless pit hate humanity and seek to destroy them, but God controls their terror and limits their power.