Of all the obscure theological terms to re-enter modern parlance, purgatory – the Catholic concept of a place of suffering inhabited by the souls of sinners too wicked for heaven, too good for hell – is perhaps most apt in our Brexit times.

Following on from his translation of Hell (published last year), Alasdair Gray has turned his attention to the second part of Dante Alighieri’s Divine Comedy. Unlike Lanark, Gray’s epic debut novel from 1981, Purgatory is a short read at around 130 pages. It is divided into 33 cantos – essentially chapters – each of which are divided in turn into three-line stanzas. The plot is linear: guided by the poet Virgil, Dante must ascend Mount Purgatory in order to be reunited with his love Beatrice. Along the way, he encounters the poor souls forced to linger in heaven’s waiting room until they are cleansed of their earthly sins. As in Hell, the narrative is littered with historical figures, for instance ‘Cato, Caesar’s foe, who stabbed himself / rather than see the Roman Empire kill / the glorious Republic that he loved.’ Reading Purgatory, written in the early 14th century, it is easy to see the crucial role Dante played in the Renaissance, when Italian artists rediscovered the glories of antiquity.

As the book’s subtitle makes clear, Dante’s medieval poem has been ‘englished in prosaic verse’ and Gray does away with the terza rima rhyme scheme employed in the original Italian. The result is a work lacking the poetic beauty of Dante’s original, with only haphazard rhyming, but rich in vivid imagery.

Dante’s voice, even when rendered into English-language prose, resonates across the centuries, occasionally addressing the reader directly in a thrilling breaking of the fourth wall. Some cantos even end in a cliffhanger, making Purgatory surprisingly readable and engaging; this is no stuffy old classic.

Gray is a mostly faithful translator, although his authorial voice is present too, as can be seen in his occasional use of Scots and British terms: highlander, wee, Tory, Whig. Such touches might please readers in the UK, but they don’t quite gel with the book’s mostly Italian cast of characters and places: Dante, after all, was born in Florence, then an independent republic. If anything, Gray is too faithful to the spirit of Dante’s original work, with his Purgatory occasionally lapsing into dull Christian moralising and reflective philosophising. “Give me your full attention now,” Virgil commands Dante, and the same is required of the reader as the poet continues: “Concentrate your analytic mind / on truth that Plato gave humanity / before Epictetus made scholars blind.”

The slog up Mount Purgatory feels at times all too real, with Dante coming across many of the same deadly sins already encountered in Hell. Matters aren’t helped by the fact that his guide remains, for the most part, the same as in Hell, until the poet Statius joins Dante and Virgil on their pilgrimage.

Where Purgatory really soars is in its final quarter, as Dante bids farewell to Virgil and ascends to the earthly paradise at Mount Purgatory’s pinnacle. Gray convincingly conveys Dante’s awe as he sets eyes on what no living human has seen since the time of Adam and Eve: “Ancient poets spoke of a Golden Age / when all was good and nothing went amiss. / Here is the former homeland of their dreams. / Nectar they sang about was in these streams.”

Part of a trilogy, Purgatory could certainly be read as a stand-alone work, although its impact would be diminished without the context of what came before. But for readers familiar with the hellish first part of Dante’s Divine Comedy, Purgatory ends up feeling slightly underwhelming. In place of the outrageous suffering and torment described in Hell, Purgatory documents the mild punishments inflicted on mild sinners. ‘Purgatorio’, as envisioned by Dante and retold by Gray, is essentially centrist: a spiritual middle ground. That is why it is most interesting at the beginning, when it still retains a degree of hell’s morbidity, and at the end, when it approaches the sublime grandeur of part three, Paradise. The middle section, meanwhile, is more slow-going, especially for readers interested in medieval history and culture.

The book cover is adorned with Gray’s charming illustration of his heroes in Purgatory, and more of these would not have gone amiss throughout. Gray should be applauded for bringing this oft-overlooked classic to the attention of modern readers in his accessible translation. However, a more radical revisioning of Dante’s original might have resulted in a work more immediately relevant to today’s times, instead of just another translation among many.