Who exactly was the black-winged deity of desire? What secrets that masterpiece uncovers about the rebellious artist

A young lad cries out while his head is forcefully gripped, a large digit digging into his face as his father's powerful hand holds him by the neck. That moment from The Sacrifice of Isaac visits the Florentine museum, evoking unease through the artist's harrowing portrayal of the suffering child from the scriptural account. The painting appears as if the patriarch, instructed by God to kill his son, could snap his spinal column with a solitary twist. Yet Abraham's chosen method involves the metallic grey blade he grips in his remaining palm, prepared to cut the boy's neck. One certain aspect remains – whoever posed as the sacrifice for this breathtaking piece demonstrated extraordinary expressive skill. There exists not just fear, shock and begging in his darkened eyes but additionally profound sorrow that a protector could betray him so completely.

The artist took a well-known scriptural tale and transformed it so vibrant and visceral that its horrors seemed to unfold right in view of you

Standing in front of the artwork, observers identify this as a actual face, an precise record of a adolescent model, because the identical youth – identifiable by his tousled locks and almost dark pupils – features in several additional paintings by Caravaggio. In each case, that richly emotional face commands the scene. In John the Baptist, he peers mischievously from the shadows while holding a lamb. In Amor Vincit Omnia, he grins with a hardness learned on the city's streets, his dark feathery appendages demonic, a unclothed child running riot in a affluent dwelling.

Amor Vincit Omnia, currently exhibited at a London gallery, constitutes one of the most discomfiting masterpieces ever painted. Viewers feel completely unsettled gazing at it. The god of love, whose arrows inspire people with often painful desire, is portrayed as a very real, vividly lit unclothed form, straddling toppled-over objects that comprise stringed instruments, a music score, metal armour and an builder's ruler. This heap of items resembles, deliberately, the geometric and architectural equipment strewn across the ground in Albrecht Dürer's print Melancholy – save in this case, the melancholic disorder is created by this smirking Cupid and the turmoil he can unleash.

"Affection sees not with the vision, but with the mind, / And therefore is feathered Cupid painted sightless," penned the Bard, just before this work was produced around 1601. But Caravaggio's Cupid is not blind. He gazes straight at you. That face – ironic and ruddy-cheeked, staring with brazen assurance as he struts naked – is the same one that shrieks in terror in Abraham's Test.

When Michelangelo Merisi da Caravaggio created his multiple portrayals of the identical distinctive-looking kid in Rome at the dawn of the 17th century, he was the most acclaimed religious painter in a city enflamed by Catholic revival. Abraham's Offering demonstrates why he was sought to adorn churches: he could take a scriptural narrative that had been portrayed numerous occasions previously and make it so new, so raw and physical that the horror seemed to be happening immediately in front of you.

Yet there existed another aspect to Caravaggio, evident as soon as he arrived in Rome in the winter that ended 1592, as a artist in his early 20s with no teacher or patron in the urban center, just talent and boldness. Most of the works with which he captured the sacred city's eye were everything but holy. That may be the absolute first hangs in the UK's art museum. A young man opens his crimson mouth in a yell of agony: while stretching out his filthy digits for a fruit, he has rather been attacked. Youth Bitten by a Reptile is eroticism amid squalor: viewers can see Caravaggio's gloomy chamber mirrored in the murky liquid of the glass container.

The adolescent wears a pink flower in his coiffure – a emblem of the sex commerce in Renaissance art. Venetian artists such as Titian and Jacopo Palma portrayed courtesans holding blooms and, in a work lost in the WWII but known through images, the master represented a famous woman prostitute, clutching a posy to her bosom. The message of all these botanical signifiers is obvious: sex for sale.

What are we to interpret of the artist's erotic depictions of boys – and of a particular adolescent in particular? It is a question that has split his commentators since he achieved mega-fame in the twentieth century. The complex past truth is that the painter was neither the queer icon that, for example, the filmmaker put on film in his 1986 movie Caravaggio, nor so completely devout that, as certain artistic scholars improbably assert, his Youth Holding Fruit is in fact a likeness of Christ.

His initial works do offer overt sexual suggestions, or even propositions. It's as if Caravaggio, then a destitute young creator, aligned with Rome's sex workers, offering himself to live. In the Florentine gallery, with this idea in consideration, viewers might turn to another early creation, the sixteenth-century masterpiece Bacchus, in which the god of wine gazes coolly at the spectator as he starts to undo the black sash of his garment.

A several annums after the wine deity, what could have motivated the artist to paint Victorious Cupid for the art collector Vincenzo Giustiniani, when he was finally becoming nearly respectable with important church projects? This profane pagan god resurrects the erotic provocations of his early works but in a increasingly intense, uneasy manner. Half a century afterwards, its secret seemed clear: it was a portrait of Caravaggio's companion. A British traveller saw Victorious Cupid in about the mid-seventeenth century and was told its subject has "the body & face of [Caravaggio's|his] own boy or servant that laid with him". The identity of this adolescent was Cecco.

The artist had been deceased for about 40 years when this account was documented.