This is one of the nine that Blake included in his one man exhibition held at his brother James's house in Golden Square, London, from May 1809 until June the following year. This exhibition was a major attempt by Blake to explain himself to the public and the exhibition was accompanied by a detailed 'Descriptive Catalogue of Pictures, Poetical and Historical Inventions, Painted by William Blake, in , Being the Ancient Method of Painting Restored: and , For Public Inspection and for Sale by Private Contract'. Fresco was Blake's term for the technique he invented which is normally now referred to as tempera. Both terms were misunderstood by Blake through lack of knowledge of Italian art. His 'frescos' or 'temperas' are painted in a form of watercolour bound together with glue, whereas true tempera uses egg yolk as the , and true fresco is watercolour painted directly into wet plaster on a wall. What matters is the significance of this technique to Blake, who believed that art, in revealing the spiritual world, should do so with the utmost clarity and sharpness. He believed that this was best done with tempera because he also, incorrectly, believed that oil painting was not invented until the seventeenth century and therefore associated it with the looser more indistinct handling of paint which developed with the style of Rubens: 'In this exhibition will be seen real Art as it was left to us by Raphael and ... Michelangelo ... stripped from the Ignorances of Rubens and Rembrandt ...' It should perhaps be added that because Blake's tempera technique is vulnerable to atmospheric changes, pictures such as this one are now rather less distinct than originally.
'The Spiritual Form of Pitt Guiding Behemoth' has a companion, 'The Spiritual Form of Nelson Guiding Leviathan' [Tate Gallery N03006]. Behemoth and Leviathan are Biblical monsters, from land and sea respectively, that Blake adopted as symbols of 'the War by Sea enormous and the War by Land astounding'. Admiral Nelson and the British Prime Minister William Pitt, were two of the leading protagonists of England's war against France at this time. Blake appears to have used them to illustrate his vision of the angels which were sent by God to destroy the world as a prelude to the Last Judgment, as prophesised in the Bible in the Book of Revelation. Pitt is accompanied by a gigantic reaper and ploughman, before whom tiny human beings flee in terror: these are specifically referred to in Revelation (Ch.14, v.v.14-19) as the angels who prepare 'the great winepress of the wrath of God'.
Simon Wilson, Tate Gallery: An Illustrated Companion, Tate Gallery, London, revised edition 1991, p.68