New Defender's Study Bible Notes
9:1 star fall from heaven. This falling (or “fallen”) star is obviously an angel, not an actual star (angels are often referred to as stars in Scripture). His name, Abaddon (Greek equivalent to Apollyon—both meaning “destroyer,” Revelation 9:11), would indicate that he is either Satan or one of the principals in the Satanic hierarchy. Satan had fallen from heaven to the earth long ago (Isaiah 14:12-19; Luke 10:18), though he still has some access to the heavenly councils as “the accuser of our brethren” (Revelation 12:10; Job 1:6-11; Luke 22:31).
9:1 key. The Lord Jesus Christ, ever since His death and resurrection, has had jurisdiction over the “keys” to Hades, where many fallen angels are confined, as well as the souls of the unsaved (Revelation 1:18). Thus, at the sounding of the fifth trumpet, He will allow Abaddon to release a horde of these demonic spirits for a five-month period (Revelation 9:5), to vent their hatred of mankind on those people on the earth who are still rebelling against God. The unsaved will have yet another incentive to repent and be saved.
9:1 bottomless pit. The word for pit, abussos (Greek meaning “without a base”) is translated “deep” in Luke 8:31 and Romans 10:7. Modern versions usually transliterate it simply as “abyss.” This pit is apparently the lowest compartment of Hades, at the very center of the earth. Its “bottomless” description can thus be taken literally, since all of its boundaries are, in effect, ceilings. It probably refers to the lowest hell, or tartarus (II Peter 2:4), where “the angels that sinned” (evidently the transgressing “sons of God” of Genesis 6:1-3) are confined in “chains of darkness” awaiting their final judgment. It is probably these that will temporarily be released by Abaddon from the bottomless pit.