It is the centrepiece, hanging between the larger paintings: The Calling of Saint Matthew and The Martyrdom of Saint Matthew.
The church commissioned the piece from Caravaggio because it was disappointed with a statue of the saint, commissioned from Flemish artist Jacob Cobaert, which was supposed to take the central spot.
The Inspiration of Saint Matthew is actually Caravaggio's second attempt at the work. His patron, Cardinal Del Monte, rejected his first effort: Saint Matthew and the Angel.
That painting showed the saint sitting casually in a chair and studying a book that's on his lap, while an angel physically guides his hand and gives him instructions.
Though many viewers and critics celebrate it as a masterpiece, the Cardinal objected to the first painting for three main reasons.
Firstly, it showed the saint as a common man with shoeless and dirty feet, while the Cardinal wanted a more idealised image. Also, he didn't want the angel to be physically imposing its will on Matthew but merely inspiring him. Lastly, he felt the image of Saint Matthew didn't match the one in Caravaggio's other two paintings of him.
Caravaggio responded to the rejection with The Inspiration of Saint Matthew. In this painting, he shows viewers a more idealised version of the saint. The viewer sees Matthew crouched over his work desk while a floating angel whispers ideas to him. The angel is wrapped in a swirling robe, increasing the sense of its otherworldliness and further distancing it from the saint.
Saint Matthew himself appears more elegant in this painting, Caravaggio having replaced his simple clothes from the first picture with elegant robes. He still manages to show the saint as someone humble and down-to-earth though, who viewers can easily relate to. The saint is still shoeless and toils at a rustic desk into the night.
Caravaggio also manages to make The Inspiration of Saint Matthew dramatic by injecting a sense of movement into the work. Saint Matthew perches awkwardly on the stool, tilting it so that one of its legs tips off the ground, in his haste to record his inspiration. He turns only his head towards the angel while his pen remains poised over the page, ready to continue writing.
The Inspiration of Saint Matthew still hangs above the altar of the Contarelli Chapel, inside San Luigi dei Francesi, along with his two other paintings of the saint.