New Defender's Study Bible Notes
20:10 brimstone. “Brimstone” was the Old English name for sulphur (“brim” developed into “burn,” sulphur being the “stone” that burns). When sulphur ignites, it burns with a very bright light and with the noxious odor of sulphur dioxide. This smell was noted by the ancients both in lightning storms and volcanic storms, so both came to be known as “fire from God”—hence the Greek words for brimstone came to be theion or theiodes. Whether or not the lake of fire and brimstone will actually incorporate burning sulphur, the use of the term indicates that the fiery lake will always be associated with the fiery judgment of a holy God on willful sin.
20:10 are. The beast and the false prophet are thus still imprisoned in the lake of fire over a thousand years after first being cast into it (Revelation 19:20). These two are actually men, of course, even though Satanically controlled men. Presumably their human bodies will be consumed by the flames when they are first cast into them, but their souls will still be there a thousand years later when Satan joins them, and they will all continue there forever. It is probable, though not explicitly so stated, that all Satan’s demonic hosts will be cast there simultaneously with him (note Matthew 25:41).