It’s a cosmic drama. At the top, a cluster of angels surround an abbreviation in Latin of the Greek name of Jesus, I H S. The H has a cross included in its design. Below, the eyes of the adoring figures on the left are drawn to the yellow glow around the trigram, representing God’s divine light. At the bottom are those farthest away from God: sinners, the unconverted, those who belong to the underworld. The mouth of hell, which is chewing them up, is portrayed as a whale-like creature with huge teeth.

This image warns viewers against sin. In the background, a bridge spans a river of fire. We are looking at Purgatory, where the souls of those who have died in sin await purification and entry in to Paradise.

El Greco’s “The Adoration of the Name of Jesus” combines the biblical themes of defending the holy name of Christ and the Last Judgment with celebration of the defeat of the Turks by the Holy League (of Christian nations) at the battle of Lepanto in 1571. We can be confident about the identity of the figures in the painting. Philip II, King of Spain, is dressed in black kneeling in the foreground. Alongside him are other members of the Holy League, the defenders of Christianity. The man with his back to us is the Doge of Venice, Alviseb I Mocenigo. The robed figure in white, blue and yellow, flanked by two red cardinals, is Pope Pius V Ghislieri. And almost certainly the man holding the sword, next to the Pope, is Don John of Austria, commander of the Holy League’s fleet. He led the Christian Spanish, Venetian and Papal ships to victory against the Ottoman Empire in 1571 at the mouth of the Gulf of Patras, off Lepanto, Greece.

But who was the creator of this apocalyptic painting? El Greco was born in Candia (now Iraklion), the capital of Crete, but spent most of his life painting in Spain. His real name was Domenikos Theotocopoulos, more popularly known as El Greco (the Greek). He probably learned to paint in Crete, looking at Byzantine art. Later he studied in Venice and then Rome.

It is not surprising that he decided to travel to Italy, as Crete was under Venetian rule from 1204 until the 17th century. His work clearly shows a mixture of influences, most especially from late Italian Renaissance and Mannerism, including such artists as Titian and Michelangelo. Supported by the patronage of the powerful Spanish Catholic Church during the Counter-Reformation (the 16th-century backlash to the Protestant Reformation), El Greco was successful as a painter in his own lifetime.

After his death, his reputation declined until his work was rediscovered in the late 19th century by artists and critics. He came to be seen as an important precursor of modern art. Distorted forms, a vivid use of colour and a lack of single-point perspective charge his compositions with energy and expression, all of which can be seen in this painting.

A larger version of “The Adoration of the Name of Jesus” is usually to be seen in the Monasterio de San Lorenzo de El Escorial in Madrid, the palace and monastery of Philip II, but is now on view at the National Gallery’s El Greco exhibition. El Greco probably painted the larger version shortly after his arrival in Madrid in 1576, to impress both the Church and the King. If the work was greeted favourably then other commissions would follow. There are several differences between the National Gallery’s own image and the Escorial picture. The most obvious is scale. The National Gallery painting is not only smaller but its dimensions are narrower.

Another variation is medium. The Escorial version is painted in oil on canvas, whereas the National Gallery painting is executed on panel using a mixture of oil and tempera. Tempera was the traditional medium for painting on wood. Ground natural pigments would be mixed, usually with egg yolk, to make an emulsion. The paint was not easy to handle, needing a slow build-up of layers to produce luminous vivid colours. Oil paint on the other hand allows the artist to be more expressive. The oil that is mixed with the ground pigments dries less quickly than an egg-yolk binder. This enables the artist to create texture and a wider tonal range.

The question of why the smaller National Gallery piece was made has been widely debated by scholars. It is not clear if the National Gallery picture is a preparatory piece for the Escorial work or was done after it, by El Greco himself, probably for use as a catalogue of his major commissions.

The sketchy quality of the painting may lead us to think it is an example or practice piece used to establish a composition and perhaps used to gain prior approval from a client before the main painting was executed.

However, even finished paintings by El Greco have the same loose brushwork.

Also, using an infrared camera, careful underdrawings can be seen, which would support the argument that the National Gallery work is a repetition of the Escorial painting.

The first major exhibition of El Greco’s work in the UK is at the National Gallery, London, until May 23. National Gallery Education invites teachers to a private view on Friday March 12, 6.30-8.30. For an invitation for two, tel: 020 7747 2424

El Greco Exhibition Book by Xavier Bray, National Gallery, pound;7.95 The Escorial version of the “Adoration of the Name of Jesus” can be seen on the Metropolitan Museum of Art, New York, website www.metmuseum.orgspecialEl_Greco1.L.htm

Karen Hosack is deputy head of education at the National Gallery, London.