"The bottomless pit" mentioned several times in the Apocalypse is not (I believe) named in any other Book of Holy Scripture. To us Christians it is revealed "for our admonition, upon whom the ends of the world are come."
Whatever other idea we may form of the bottomless pit, whatever other feature we may think to detect within its undefined horror, two points stand out unmistakably: as a pit it is a place into which to fall; as bottomless, it appears to be one within which to fall lower and lower for ever and ever.
Herein lies one distinct thought for ourselves: an awful thought. A deep fall, indefinitely deep, so long as any bottom at any depth underlies the lapser, must at length be arrested and must stop. However mangled or shattered, and on whatever floor landed, the wretch cannot cease there to lie: self-destroyed, indeed, yet accessible to Mercy and Help if these deign to look so low, and lift with recovering hands, and carry home on shoulders rejoicing.
But in the bottomless pit I see a symbol of that eternal antagonism and recession by which created free-will seems able to defy and baffle even the Almighty Will of the Creator. At a standstill anywhere, though on the extreme boundary of time or space, the sinner might be overtaken by the pursuing Love of God: but once passing beyond those limits, eternity sets in; the everlasting attitude appears taken up, the everlasting recoil commenced.
Beyond the grave no promise is held out to us of shipwreck, great fish, dry land, to turn us back towards the Presence of God from our self-chosen Tarshish.