What is the importance of the Rokeby Venus by Velazquez in the novel, War and Turpentine?

The Rokeby Venus by Velazquez is a painting that shows its head multiple times over the course of the novel as an object that preserves forbidden love. Urbain preserved his image of the dead Maria Emelia in his rendition of the painting, weeping over it in the future, despite his long marriage to Gabrielle.