Setting is extremely important to Paradise Lost as a whole. The poem rests on the contrasts between the great stages of Heaven and Hell with the young Earth in between. Heaven is all light, purity and glory, but it is Hell which is more vividly described by Milton, and nowhere more so than in the first book, which memorably sets the scene for the poem's central action: the ongoing rebellion and plotting by Satan against God, which has such momentous consequences. The opening description of Hell, seen from Satan’s point of view, conjures up a strange picture:
At once as far as angels’ ken he views
The dismal situation waste and wild,
A dungeon horrible, on all sides round
As one great furnace flamed, yet from those flames
No light, but rather darkness visible
Served only to discover sights of woe …
Along with fairly straightforward references to Hell as a vast, desolate prison, we get the striking description of its flames of darkness rather than of light. It radiates darkness and despair rather than light, as in Heaven. This description is effective on both the literal and metaphorical level: Hell's fiery dark miseries also reflect its inhabitants’ despairing state of mind at having lost their heavenly station. Most anguished of all is Satan, their leader; amid all his pride and defiance this despair never quite leaves him.
Satan's state of mind is also connected to the setting in later books, as in Book 9, where Eden appears as a place of exquisite sweet grace and innocence - the kind of qualities that he himself has lost for ever. The contrast between the serene beauty of the setting at this point and his inner torment is quite marked; at the same time he is planning to infiltrate himself into this place of innocence and grace and defile it.
Eden again is the main setting in Book 12 and once more Milton plays up the connection of setting to the state of the characters. By this point, Adam and Eve have fallen into sin and disobedience, and Eden has been despoiled, although it retains its fair aspect. Now Adam and Eve will have to leave it for ever. However, they are comforted somewhat by the angel Michael who reassures them that in future mankind will be redeemed through Christ. They will take the solace of this knowledge with them. Therefore, although they will be removed physically from Eden, they have gained ‘a paradise within … happier far’. Paradise, has, in effect, become internalized for them, just as earlier Satan had lamented ‘Which way I fly is hell; myself am hell’ (Book 4). The settings of Paradise Lost, then, are not just vast physical realms, but also symbolic of the inner states of its characters.