In Room VIII of the Pinacoteca at the Vatican Museum in Rome hangs The Transfiguration, the last painting made by Raphael before he died from a fever at the age of 37. Giorgio Vasari, the biographer of the Renaissance masters, described this painting as “the most famous, the most beautiful and most divine” of Raphael’s works.At the top of the altarpiece (commissioned for the Narbonne Cathedral, but apparently deemed too good for the Pope to let it go), Christ floats in glory above Mount Tabor, flanked by the prophets Moses and Elijah, their robes billowing in the holy turbulence, while the disciples lie where they have fallen in astonishment at the mountain’s peak. The lower part of the painting depicts an event that happened earlier the same day — the failed attempt by the apostles (on their way up the mountain) to cure a possessed boy who stands, eyes boggling, on the right.

It’s an exceptional image for a number of reasons, not least because at the time of its making this intersection of two consecutive narratives in a single painting — and their successful unification, using light and the play of gesture and expression — was new. Full of life and movement, it perfectly balances the visualisation of man transforming into divinity and the engrossing action required to hold the attention of the less high-minded faithful. And, as I discover once I’m back in Britain, sitting in the prints and drawings room of the Ashmolean Museum in Oxford with Dr Catherine Whistler, the keeper of the museum’s Western Art Department, it’s also knocked into a cocked hat by its preparatory drawings.

One drawing in particular, which will be the star of the Ashmolean’s forthcoming exhibition, Raphael: the Drawings, of which Whistler is the co-curator. Rather than look at the drawings in the way that they are usually studied — as adjunct material to the paintings — the show will explore how Raphael used drawing as a mode of thinking about the body, storytelling, emotion and psychology, beauty and grace.

Split into three broadly chronological themed galleries — inventiveness, orchestration (using drawing as an ideas generator and a design tool) and expression) — it follows Raphael from his birthplace, Urbino, to Florence. There he encountered classical and early Renaissance sculpture and also, it is clear from a sheet in the exhibition depicting the head of an enigmatic youth and the face of a jowly old man, directly studied the drawings of Leonardo da Vinci. He then went to Rome, where he quickly secured a significant fresco commission at the Vatican and his career took flight.

Back to that preparatory drawing, however (although this highly finished work is more than a functional object and as Whistler says, “We know that Raphael did on occasions make gifts of drawings, specifically when he was being chased for paintings”). Known as The Two Apostles, it’s a large-scale study in black chalk depicting the heads and hands of two of the disciples in the lower scene of The Transfiguration, one young, one old. It is, as Whistler says, “a real wow drawing”.

The pity expressed in that single line is almost miraculous. It’s also impossible to paint

Whistler says: “They’re looking, remember, at the boy, who is not being cured, because [the image] is about failing. Christ is not with them below the mountain, and they are caught up in the emotions they feel — looking at this boy and his family but also thinking, ‘We’re meant to be the apostles, why can’t we help?’ ” Peering at the drawing up close, you’re drawn to a heavily shaded line below the right eye of the younger apostle. The softness of the skin, the tiredness, the pity and anxiety expressed in that single line is almost miraculous. It’s also impossible to reproduce in paint.

“It’s quite complex, what Raphael is trying to do here,” Whistler says. “It’s about trying to understand the emotional states, the psychological states of these sacred protagonists.” Yet in turn, that also relates to Raphael’s status as a gentleman in 16th-century Italy. Born in 1483 around Easter time, Raphael was the son of a painter and courtier, Giovanni Santi, whose workshop was patronised by the city’s sophisticated ducal court. Raphael grew up in an environment where learning and artistic empathy were highly valued.

A gentleman’s education in Raphael’s day was mapped on to ideas found in Cicero and Quintilian’s writing about the orator. “What the orator has to do, in order to communicate and to successfully make his audience really feel, is to actually experience the emotions that he wants to communicate, and that’s what Raphael is doing in drawing,” says Whistler. “And, yes, it provides a wonderful tonal guide to how the features will be painted, but so much more is going on here than in the painting; so much more is captured in this very elaborate drawing.”

Another aspect of this that is expressed through Raphael’s drawings relates to the idea of sprezzatura, a desired characteristic of the courtier defined by the word’s inventor, Baldassare Castiglione, as “a certain nonchalance which conceals all artistry and makes whatever one says or does seem uncontrived and effortless”. Raphael had sprezzatura in spades, as can be seen in a drawing of Hercules overpowering the Nemean lion from about 1507-08, when the artist was still in Florence.

The drawing doesn’t relate to any known work and Whistler notes that at this time the idea of a drawing as an artwork of value in its own right was gaining ground. Talking me through the sheet, she shows me a flurry of indented lines delineating the basic image, barely visible to the naked eye, but which appear when the paper is shown in a strong, raking light.

“There’s quite a lot of sketching first with a stylus that doesn’t leave marks but indents the sheet. That’s something we’ve seen more and more of as we’ve been looking at the drawings more closely. Raphael does this very free drawing first, getting his thoughts on to the sheet, and then he takes up the pen and starts developing the image.”

The final pen strokes, though artfully “unfinished”, give a clear impression of the movement of muscles beneath the skin, the momentum of the attacking hero, and the ferocity and wildness of the lion. The artist makes it look easy, dashed off even, but underneath it has been carefully planned. That there is much more of this secret, invisible effort found round the figure of the lion indicates how familiar Raphael was with the classical, heroic male nude, and not with rampaging lions.

Raphael’s courtly bearing and intelligence did much to recommend him to influential patrons. Vasari pointedly compared him with the notoriously awkward Michelangelo, saying that Raphael “was as excellent as gracious, and endowed with a natural modesty and goodness . . . and he always showed himself sweet and pleasant with persons of every degree and in all circumstances. Thus Nature created Michelangelo Buonarroti to excel and conquer in art, but Raphael to excel in art and in manners also.” Yet it was Raphael’s virtuosity that kept him in business. This was quickly noted by Pope Julius II, who, when the 25-year-old painter arrived in Rome, almost immediately expanded his commission to include four rooms in his private apartments.

This support and reverence for his skill gave Raphael the freedom to innovate in a way that many painters couldn’t. The exhibition will include a couple of drawings that relate to his 1507 Deposition (aka the Borghese Entombment), which was commissioned by the powerful matriarch Atalanta Baglioni for San Francesco al Prato in Perugia. It picks up a common subject, the lamentation over the dead Christ, that had also been tackled by one of Raphael’s early influences, Perugino.

There is a perception that he’s a bit bland, but there is a power in the drawings

Using the same cast of characters, however, “Raphael does something utterly different in terms of movement and emotion”, says Whistler. Taking his inspiration (as can be seen clearly in the drawings) from an ancient sarcophagus relief of the death of Meleager, he transforms Perugino’s static tableau into a dynamic, vivid scene — the men strain under the palpable weight of the dead body, which has a disconcerting greenish tinge, the Virgin is caught in the act of fainting, while the Magdalene lurches compulsively to touch Christ’s face. Blood streams from his wounds. It is bold, it is startling and it is risky.

“He’s treading a fine line of decorum,” says Whistler. “Raphael is trying to create a drama, which is to do with the strain involved in bearing a dead body, but a dead body that is resonantly the body of the saviour, who is going to be resurrected. He creates in that altarpiece an extraordinary piece of religious theatre, in the reactions of the women, the tenderness, the swooning, by contrast with the stress and strained bodies of the men. That is really pushing the boundaries.”

This movement from paintings considered as purely devotional items to works of art would later trouble the Catholic Church, leading to strict guidelines and restrictions on experimentation in public works of religious art, but Raphael, one of its pioneers, would be long dead by the time the Council of Trent was having underwear painted over the nudity in Michelangelo’s Last Judgement.

Drawing, however, is the place where we can see Raphael at his most free. Whistler shows me a couple of the earliest images in the show, made when Raphael was 16 or 17 years old. On one he sketches a back view of a figure from a Luca Signorelli painting, a male nude pulling a crossbow — you can see him relishing the serpentine flow of the body as the muscles tense. On the other sheet the same figure reappears (quite sketchily done — he’s clearly thinking mostly about buttocks), but then he turns the sheet around and fires off five or six ideas for increasingly whimsical, curlicued and be-cherubbed frames. “And then he turns the sheet again and there’s the head of a unicorn. This is drawing as pleasure, and playing with ideas,” Whistler says. It’s a delight to observe.

The hope, says Whistler, is that visitors to the show will find that Raphael “is a much more adventurous, experimental, interesting artist than you might have thought. People tend to think about Raphael by thinking about idealism or sentimentality. There is a perception [that he’s] a bit bland, he’s not really relevant, but there is a power in the drawings.” They provide a direct line to the artist, and frankly if that line under the apostle’s right eye doesn’t touch your heart, then I don’t know what will.