Paradise Lost ; by John Milton

The subject of Paradise Lost is Man's disobedience and the ensuing loss of Paradise on earth, but its theme in the simplest term is love. The central episode of Satan's revolt against God and his defeat by the Son is illuminated as the origin of the difficulties which Man will experience (though not yet created) and as continuous admonition of Satan's defeat before, during, and at the end of mortal time.
The justification of God's ways lies in the demonstration that man can learn the nature of God only by knowing the nature of evil, that he can rise only by first having descended, and that obedience is the natural consequence of love.

The character of Satan strikes us as the most impressive figure in Paradise Lost. The poet's great achievement lies not only in the portrayal of the majestic figure of Books I and II but in the slow and steady degeneration of the "arch fiend" into a slimy, deceitful serpent. The portrayal of Satan in the first two Books is such that a controversy has cropped up about the hero of this epic. Many critics have taken Satan to be the hero. This misinterpretation, perhaps, is due to the fact that such a view is based on the reading of the first two books only. In fact the hero is Adam - a tragic figure in many ways. Adam's character, though not as dynamic as Satan's is nevertheless very finely etched. Adam's role is not that of a warrior (which Satan is) but that of a God fearing man, faced with temptation and defeated in the conflict between himself and Satan. But the defeat is not final. Adam regains the Paradise "happier far".

Neither God nor the Messiah takes part in the central action of "Paradise Lost". It is true that Adam has a somewhat passive role as well but the fact remains that the whole epic turns round 'man's first disobedience'. Adam disobeyed God, and by this act of disobedience, he not only lost Paradise but brought about the fall of the while human race. No action can be more tremendous in its import and significance than that which brought the fall of the whole of humanity. And Adam being responsible for it, is obvious meant by the poet to fill the role of the hero of the great poem. Ultimately, Adam and his race come out triumphant by the grace of God and regain the lost Paradise. 

The last twenty lines or so of the poem describe Adam and Eve's departure from the happiest place on earth (no, not Disneyland, that hasn't been built yet). They are crying as the gate is closed and a flaming brand is placed over it. This is the end of a pain-free, immortal life for humans. Paradise has been lost.