John Milton was an exceedingly learned classical and biblical scholar, the author of a treatise against censorship, and a passionate believer in the importance of rational free choice in matters of conscience.
After the Civil War, Milton is employed by the Parliamentary regime which defeated and executed King Charles I; he defends the Parliamentarians' actions in print and for many years handles their diplomatic correspondence with foreign powers (despite his encroaching blindness).
He completes Paradise Lost (first published 1667) after his enforced retirement from public life when the monarchy is restored.
An epic is usually defined as a long narrative poem celebrating the great deeds of one or more legendary heroes in an elevated and ceremonious style.
You'll recall that epics are often stories of origins: Milton recounts the story of the Fall--from a Christian point of view, the story of the origin of the whole human condition--and in so doing threatens to pre-empt or render secondary all other epic narratives.
Note that since epic narratives tend to privilege warrior virtues, a Christian epic is probably going to have to revise epic convention (Christ's own "heroism" has little to do with aspiring to earthly glory or conquest).
Lines 1-26 suggest how difficult it is to begin the Narrative of Beginnings.
Here we see the perilous nature of the Miltonic project: in seeking to supplement the Word of God, he may himself risk "falling" should his recreation of Genesis lack divine inspiration.
The prehistory of the fall of humanity is the fall of Satan.
These are indeed an unholy trinity, whose relations are a travesty of those between God, Adam and Eve. Please take note of the following:
In a poem that is fascinated with beginnings and acts of authorship, Satan is the father of lies, the original false artist and revisionary historian, a creature who tries to usurp God's role as creator but who can only father Sin and Death.
Satan at I.250ff. vs. Satan at IV.75ff. (Remember Marlowe's devil: "Why, this is hell, nor am I out of it.") The mind is its own place, and that is why Satan is stuck in hell even when he is geographically on the very threshold of Paradise.