Poets are notoriously ill-paid. Words are cheap, and in the age of social media they're even cheaper. But still, a mere £10, paid on this day around 350 years ago for what's recognised as one of the finest works in the whole of English literature, seems a little unfair.

In 1667, however, it was worth quite a lot more. According to Measuring Worth, the publishing rights to John Milton's Paradise Lost would, in today's money, have gone for at least £1,625 and possibly as much as £31,380, depending on how you calculate it. Since it's sold millions of copies since, the higher figure is probably the fairest.

Having said that, it's not a work most people actually read: 12 books of blank verse, full of learned references not just to the Bible but to classical mythology, aren't everyone's cup of tea. But at its best it is a gripping, thrilling read – and arguably particularly when Milton is talking about Satan. For some commentators that's been seen as a bit sinister – how can a Christian write his best work about the Devil, and be frankly a bit boring when he's writing about God? Perhaps it was his Republicanism – he was a Protestant who was on Parliament's side in the Civil War that resulted in the beheading of Charles I, and some people never forgave him for it.

But more likely is just that he had an extraordinarily vivid and powerful imagination. And his picture of Satan as a ruined angel, fallen but still magnificent, a mighty power cast down from heaven but ominously potent still, casts a long shadow.

What does Milton say about Satan? His motive for rebellion is pride, that led him to 'set himself in glory above his peers' and to be the equal of God himself. His temptation of Eve is out of 'envy and revenge' at his punishment – and his torments in hell are vividly described. Hell is:

A Dungeon horrible, on all sides round
As one great Furnace flam'd, yet from those flames
No light, but rather darkness visible
Serv'd onely to discover [reveal] sights of woe,
Regions of sorrow, doleful shades, where peace
And rest can never dwell, hope never comes
That comes to all; but torture without end
Still urges, and a fiery Deluge, fed
With ever-burning Sulphur unconsum'd.

And Milton imagines Satan as being huge, like the sort of Leviathan seafarers mistake for an island:

So stretched out huge in length the Arch-fiend lay
Chain'd on the burning Lake...

He rises and flies heavily to the shore:

...till on dry Land
He lights, if it were Land that ever burn'd
With solid, as the Lake with liquid fire...

Then comes the great soliloquy in which Satan reflects on what he will do next. He won't repent, for sure – and at least in hell they will be left alone. After all:

The mind is its own place, and in it self
Can make a Heav'n of Hell, a Hell of Heav'n.

And in the classic statement of where pride and self-will can lead, he says:

Here we may reign secure, and in my choice
To reign is worth ambition though in Hell:
Better to reign in Hell, then serve in Heav'n.

He has talked himself into eternal warfare. Supporting himself with a spear taller than the mast of a ship, he walks with 'uneasy steps' across the burning soil to the shore of the lake of fire where the fallen 'rebel angels' are still wallowing, as thick as fallen leaves, and calls them to arms with a voice of thunder. All the demons that torment mankind with violence, lies, lust, deceit and terror spring to attention: 'Ten thousand banners rise into the air.'

What will they do? After bursting into 'tears such as angels weep', he urges them to war.

He spake: and to confirm his words, out-flew
Millions of flaming swords, drawn from the thighs
Of mighty Cherubim; the sudden blaze
Far round illumin'd hell: highly they rag'd
Against the Highest, and fierce with grasped arms
Clash'd on their sounding Shields the din of war,
Hurling defiance toward the vault of Heav'n.

And the rest is history, or at least theology. Satan and his council resolve to ruin the new and beautiful earth God has made by tempting Adam and Eve. Their success leads to Paradise Lost; but there is a sequel, Paradise Regained.

What the first two books of the poem in particular offer is a full-blooded depiction of evil as a mighty power opposed to everything good and godly. Of course Milton didn't think he was depicting real scenes – but he was convinced of the reality of Satan and of evil. That imaginative power still carries conviction today – and the writing is wonderful.

Follow Mark Woods on Twitter: @RevMarkWoods