Context: Milton asks his epic question, who seduced our original parents into disobeying God? The answer is, the infernal serpent, whose pride had cast him out of heaven; with him there fell a host of rebel angels. Satan, motivated by envy of God and by the desire to be revenged on Him for what he considered injustice, deceived Eve, the mother of all mankind. For his revolt, God hurled him and his cohorts out of heaven, down to bottomless perdition, there to dwell in adamant chains and penal fire. Milton here was probably drawing on the classical account of Zeus's hurling of the defeated Titans into the underworld, where they were perpetually imprisoned. Milton, however, quickly abandons the idea of the unbreakable chains–if he ever had it–as the devils are free to travel through the universe, especially up to the earth. But for nine days the devils lie stunned on a fiery lake. "Ken," usually "knowledge," is here "range of view."
Nine times the space that measures day and nightTo mortal men, he with his horrid crewLay vanquished, rolling in the fiery gulf,Confounded though immortal: but his doomReserved him to more wrath; for now the thoughtBoth of lost happiness and lasting painTorments him; round he throws his baleful eyesThat witnessed huge affliction and dismay,Mixed with obdúrate pride and steadfast hate:At once as far as angel's ken he viewsThe dismal situation waste and wild,A dungeon horrible, on all sides roundAs one great furnace flamed, yet from those flamesNo light, but rather darkness visibleServed only to discover sights of woe,Regions of sorrow, doleful shades, where peaceAnd rest can never dwell, hope never comesThat comes to all; . . .