Great Works: The Adoration of the Kings 1564 (111.1 x 83.2cm), Pieter Bruegel the Elder

National Gallery, London

How "authentically" have the great painters evoked the birth of that miracle-working God man Jesus Christ of Nazareth? And does the idea of authenticity itself really make any sense anyway? Two particularly fine examples of Nativity scenes hang in London's National Gallery. The first is by the great Quattrocento Italian artist Piero della Francesca. They could not be more different from each other.

By and large, we could say that it has been the Italian habit to idealise the birth of Jesus – which is perfectly understandable given the nature of the subject matter, and the fact that the Vatican is in Italy. Who would not wish to represent what the culture commonly regards as a superhuman act in a manner that emphases its super-humanness? And yet the whole point of Jesus Christ, according to Christian belief, is that he was just as much man as god, and so to emphasise his supernatural nature wholly at the expense of his humanity, is to idealise one step too far...

Piero della Francesca's Nativity of 1470-5 hangs in a room that feels like a small, hushed, sacralised space. On the right hand wall hangs a gloriously reverential, monumentally serene nativity, in which the slender young virgin kneels in homage before her baby as an angelic team of lutinists and choristers process towards us, hymning, open-mouthed, the virgin's awe-struck, motherly response to the divine birth. So much for the religious content. The human factor is represented by the locale in which the scene is situated: it's a Tuscan spot – there's a Tuscan hill town on the horizon, a fairly decrepit Tuscan cow byre, and a thumpingly large Tuscan magpie. A sweet, yellow evening light is gently falling. Not a breath of chilling winter wind anywhere.

Over in Gallery 14 hangs Pieter Bruegel the Elder's The Adoration of the Kings. This was painted in 1564, Michelangelo's death year, and Bruegel has signed and dated it, scratchily, in Roman numerals, at bottom right. The sight of this signature pleases. It is tangible evidence of the living, breathing presence of a painter who was always so breathingly, broodingly, bruisingly present in every painting, drawing and etching that he ever made – there was nothing hands off about Bruegel. Nor is there anything ethereal about this Nativity scene. In fact, it feels, in spite of the fact that its ostensible subject matter is the giving of the gifts, almost shockingly set apart from devotional sentiment.

This painting is entirely about the close scrutiny of human behaviour. Ideas of the divine barely get a look in. It is an amusing, intriguing, deflating look at what may have happened when the three kings came to pay homage to the infant with their gifts of gold, frankincense and myrrh. We expect of a Nativity scene that the onlookers will be wholly focused upon the central mystery of the birth of the child, that the revered bambino will be surrounded by a kind of invisible aura. This doesn't happen here. Most of the onlookers are looking in different directions – at each other, at the astonishing gifts, at the even more astonishing presence of these elongated strangers, so wizened of face, with such lank and greasy hair, in their extravagantly colourful regalia.

The single most beguiling detail is a wonderful red, pointed boot worn by the black king on the right whose head is tricked out in a white bandana, and who also happens to be carrying the most curious of offerings – a gold boat evidently made by some master goldsmith, inside which sits a nautilus shell from which a mechanical monkey is emerging. Even stout Joseph is half distracted by the man who whispers a confidence into his ear. So our eye is constantly shifting all over the place, trying to see what each individual – and they are wholly individualised, each one – is so fixated by, trying to understand why the crowd consists, for the most part, of armed soldiers with their halberds, swords and crossbow at the ready. Bizarre in the extreme. Now look at that tiny man-child of an ugly baby. He too is behaving wholly uncharacteristically. He seems to be recoiling in horror from the gift of myrrh. Perhaps he is right to do so. Myrrh, after all, is used for the embalming of bodies. Or perhaps he is shrinking back from a face of extreme ugliness. Everything looks so secular here – expect perhaps for the look on the face of the virgin. She at least is behaving in a passably religious way, although the look on her face may merely be evidence of post-natal exhaustion. And what are all these soldiers with their fierce weaponry doing here anyway? Are they the hateful Spanish soldiery whose presence would still have been haunting Bruegel's homeland?

In short, this is a Flemish village scene. It is also, it could be argued, a lavish display of gloriously unflinching mockery at the expense of religion.

ABOUT THE ARTIST

Pieter Bruegel was born in a village to the east of Antwerp in 1525, and died in Brussels in 1569. Best known for his crowded and rumbustious scenes of Flemish peasant life, he was greatly influenced in his compositional methods by Hieronymous Bosch. His canvases consist of crowded spectacles of teeming human life that take in baseness, disorder and hilarity.