In 1964, Kenneth Clark set out the problems of loving John Ruskin. One was his fame itself. Like his sometime pupil Oscar Wilde (who, along with other of his Oxford students he persuaded to dig a road in Hinksey in order that they learn the dignity of labour), Ruskin defined the art and culture of his century. “For almost 50 years,” Clark wrote in his book, Ruskin Today, “to read Ruskin was accepted as proof of the possession of a soul.” Gladstone would have made him poet laureate “and was only prevented from doing so by the fact that [Ruskin] was out of his mind”.

Ruskin was a man who believed in angels but championed the most radical British artist of his time. He was a social reformer and utopian who was at heart a conservative reactionary and a puritan. He was a brilliant artist who ought to have been a bishop. He hated trains but invented the blog.

How can it be that a man so celebrated in his time is only fitfully remembered now, 200 years after his birth – and then mostly for a salacious story that he was too intimidated by the sight of his young wife’s pubic hair to perform on his wedding night? He’s a beardy Victorian worthy, preserved in sepia photographs and unread books with inexplicable titles – Unto This Last, Sesame and Lilies, Praeterita – consigned to the top shelves of charity shops.

The problem lies in the fact that Ruskin rejects all those presumptions even in his own lifetime. His watercolours of the natural world – from mosses to Swiss mountains – are astonishing, hyper-real representations of something close to his soul, a metaphysical reality. He declined to join the headlong rush of economic progress and rejected the mores of his class. In the famous portrait of him by John Everett Millais – the Pre-Raphaelite artist who, even as he painted the picture in the Scottish Highlands, was about to seduce Ruskin’s young wife, Effie Gray – he stands on a rock by a waterfall, as if dominating the terrain around him. He looks the picture of Victorian rectitude; but he was undermining the century with his crusade.

His first offence was to champion William Turner’s paintings. Almost intuitively, Ruskin understood the power of what Turner was trying to do. As the contemporary eco-philosopher Timothy Morton says, “art is from the future”; Ruskin saw that futurity in Turner. His second offence was to attack capitalism. As Clark notes, Tolstoy, Gandhi and Bernard Shaw thought him one of the greatest social reformers of his time. When members at the first meeting of the Parliamentary Labour Party were asked which book had most influenced them, they answered Ruskin’s Unto This Last. Bernard Shaw pithily summed up Ruskin’s affront to his own class: he told them, “You are a parcel of thieves.”

Art and revolution: Ruskin’s violent social conscience was as absolute as it was paradoxical and sometimes surreal, given that he relied entirely on inherited wealth. In 1874 he set up a tea room in Marylebone in which he hoped to install his beloved Rose La Touche, just one of the young women with whom he fell in love. At the same time he was sending out monthly newsletters to the working man, exhorting him to take note of the work of Albrecht Dürer and blasting the appalling poverty he saw in mid-19th-century Britain. These extraordinary samizdats were the forerunners of the blog – only with more soundbites and psychodrama. “THERE IS NO WEALTH BUT LIFE”; “Gunpowder and steam hammers are the toys of the insane and paralytic”; “Meanwhile, at the other end – no, at the very centre of your great Babylon – a son leaves his father dead, and with his head, instead of a fire, in the fireplace…”

Ruskin was, after all, brought up to be a priest; he delivered his first sermon to the family as a young child – it began, “People, be good.” His parents were of Scottish descent and in trade – his father a sherry merchant and his mother the daughter of a publican. But they had money and travelled around Europe in a custom-built coach; Ruskin remembered that it had comfortably rounded corners to its interior woodwork.

These trips were the means of Ruskin’s epiphany: when he saw the Alps, his life changed. He knew the importance of art – in its record of nature. He went up to Oxford, but his mother came too – they took tea together every evening. In his late teens he fell in love with Adèle-Clotilde Domecq, daughter of one of his father’s partners, but her Catholicism meant a match was impossible. Ruskin turned for consolation to his love of the works of Turner, whom he met in 1840. The feeling wasn’t mutual; the painter actually preferred the company of Ruskin’s father, having been freaked out by John’s description of him as “the great angel of the apocalypse”.

It was the birth of the named, as opposed to anonymous, art critic. But the “strange afflatus” in those blue eyes (he customarily wore a blue silk stock to reinforce the effect) betrayed an incipient instability. “Genius is made more comprehensible by a medical diagnosis,” Clark wrote, noting that Ruskin probably suffered from manic depression.

A semi-arranged marriage to Effie Gray was never going to work. She had no interest in being the domestic wife Ruskin wanted, and she didn’t appear to excite him sexually either – although the notion that he had been aghast at her pubic hair now seems to be a smear. Tim Hilton, author of the best biography of Ruskin, suggests that Effie may have been menstruating on their wedding night; he also sees Ruskin’s offer to divorce his wife and sacrifice his own reputation as the act of a gentleman.

Ruskin followed this disaster with his infatuation with Rose La Touche. She was ten when they met; he was 38. Their pathetic story ended in her early death, problably from anorexia, and his insanity. Ruskin withdrew into his madness; his genius was withdrawn from us. He died on 20 January 1900, as if to end the century himself.

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You can still visit the turret of Ruskin’s bedroom, from which he looked out one night over Coniston Water and lost his mind. Brantwood, the house that Ruskin bought in 1871 and extended into a gothic pile, hangs darkly over the still lake. It is a somewhat Wagnerian scenario; you can even arrive by a gilded steam gondola.

It was from this eyrie that Ruskin had continued his utopian experiments. He created a hillside garden as a simulacrum of the natural world with which he so empathised, as though it were a reflection of his own body, the human physicality he could never reconcile with his dreams, with the spirit world or the even more intense world of aesthetics. He decried the craze for gothic – which he knew he had partly inspired, but which had resulted in the replication of a million gothicised suburban villas – as a personal betrayal of his vision of The Stones of Venice. His Guild of St George called for England’s renewal in colonies in the countryside. Workers would be paid fair wages and taught music, art and morality, along with “gentleness to all brute animals. It is not to be Communism,” he insisted, “[but] the old Feudal system applied to do good instead of evil.”

All this was directed from Brantwood, his northern palazzo, where he waited for the ominous storm-cloud of the 19th century to drift from the industrial oppression of Manchester and Bradford. He would row out into the middle of the lake and lie on his back looking at the sky, or play his self-invented stone xylophone, another physical evocation of the hard landscape, turning the Lake District into a musical instrument.

None of this kept the madness away. He dabbled with mesmerism. In Venice he felt the ghost of Rose La Touche, like a pre-echo of Don’t Look Now. He engaged mediums and summoned La Touche in seances, and saw her coming to him, in marriage, with Joan of Arc as their priest.

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You may also come face to face with Ruskin’s ferocious intelligence at a new exhibition, The Power of Seeing, at London’s Two Temple Place – a selection of Ruskin’s works gathered in the grand mock-medieval interior built for William Waldorf Astor as his estate office.

Curated with Museums Sheffield and the Guild of St George, which carries Ruskin’s torch into the modern world, The Power of Seeing displays, beautifully and intimately, the artist’s evanescent watercolours and fugitive daguerreotypes (he copied them on vast posters so that his audience “might not be plagued in looking, by the lustre”). They are set alongside works by Turner, as well as diaries, plaster casts and two bizarre giant wooden birds’ feathers – like enormous quill pens – created as props for Ruskin’s public lectures by the taxidermist and animal preserver WF Davis.

The exhibition evokes the overstuffed museum that Ruskin installed at Walkley, outside Sheffield, supervised by one of his acolytes, Henry Swan – spiritualist, vegetarian and boomerang thrower – who “lectured visitors as if he were the speaking voice of Ruskin’s own books”. But then, his own master’s eccentric crusades still reverberate, as he declared himself – in his Scottish burr – to be against cycling, which joined train travel as one of the blasphemies of modern society: “I not only object, but am quite prepared to spend all my best ‘bad language’ in reprobation of the bi-, tri- and four-, five-, six-, or seven-cycles…”

Perhaps most moving is a corner dedicated to Ruskin’s worship of Dürer – Albert, as he called him, confidingly. The German artist’s enigmatic engraving Melencolia I hangs as kind of memento mori of Ruskin’s own melancholy. Yet that same instability turned his lectures into electric performances worthy of Joseph Beuys. Ruskin waved around his giant flowers and leaves like pop-art icons, and would strut across the stage in imitation of one of the birds whose beauty he was extolling, demonstrating its flapping wings with his cape.

These events were sell-out occasions, but whether people attended for their moral education or to witness the extreme behaviour of someone who was clearly mentally unwell, it is not easy to say. Set this furore against the quietness of his nature studies and you feel Ruskin’s beautiful, wanton mind: in a piece of frozen seaweed, a microcosmic vista of lichens and ferns as if lit by the moon; or a bit of crumbling brick with moss growing on it, rendered in such detail that it hurtles towards you like an asteroid. It now seems like the last of England, this exquisite art, somehow symbolic of Ruskin’s synoptic, apocalyptic aesthetic.

In her brilliant little book – published to coincide with the 200th anniversary of Ruskin’s birth – To See Clearly: Why Ruskin Matters (Quercus), art historian Suzanne Fagence Cooper makes plain why he does. Ruskin saw more clearly than most – more clearly than most critics, especially – because he was an artist. He believed that just as anyone can learn mathematics or another language, so they can draw; it was only a matter of practice – and of looking.

He was, after all, a man who thought nothing of spending five hours just looking at the sea (he even upbraided Turner for being too conventional; the artist’s water wasn’t wet enough) and who religiously made sure he witnessed the sun rise and set every day. Ruskin exhorted pupils to draw a stone: not to start with an outline of it, but to look at the way the light fell and render those patches in impressions of its stoneliness. “Now if you can draw the stone rightly,” he said, “everything within reach of art is also within yours.”

The art historian Robert Hewison observed that Ruskin’s puritanical religion directed him away from the problematic human body into the natural world; hence Mike Leigh’s portrayal of the critic in his 2014 biopic Mr Turner as a simpering, sexless thing. But Ruskin is far more than a nature lover. He is a man who could see a mountain in a stone and make us believe it. We need him more than ever as we find ourselves evermore distanced from the world. At the height of his art and his humanity, Ruskin brings us vertiginously, exquisitely closer to what really matters. There is no wealth but life.

“John Ruskin: The Power Of Seeing” runs until 22 April at Two Temple Place