Paradise Lost is a poem in 12 books based on the biblical story of Satan's fall from heaven and Adam and Eve's sin in the Garden of Eden. Milton's strong Puritan faith is evident in all his work and comes to its greatest height in the epic poems. The opening lines of Paradise Lost give the “argument” for the piece in which Milton invokes the heavenly muse to help him write:
"Of Man's first disobedience and the fruit Of that forbidden tree, whose mortal taste Brought death into the world, and all our woe, With loss of Eden, till one greater Man [Christ], Restore us and regain the blissful seat, Sing, O heavenly Muse…”
Like John Bunyan’s The Pilgrim’s Progress, Milton’s Paradise Lost “fills in” details of what takes place in the spiritual realm. Milton presents interactions between God and Satan, Satan and Adam and Eve, Satan and his demons, etc., using poetic license and lyrical expression. Nothing in Paradise Lost directly contradicts the Bible. But Milton's work should not be understood as biblical fact. Perhaps the most famous line from the poem is Satan’s rebellious declaration, “Better to reign in hell, than serve in heaven.” So often has that line been repeated that it is often mistaken for a quote from the Bible.
It should be noted that Milton’s poetry can be difficult for the modern reader. Paradise Lost is full of the rhythms and idioms of 17th-century English, and Milton often alludes to Greek mythology and Renaissance Italian, French, and English writers, many of whom are unfamiliar to the modern reader. But, from a theological and literary standpoint, his work is first-rate. Amazingly, Milton wrote his poem while completely blind, having to dictate the lines to his secretary.