The painting, dated 1620 and destined for the Locatelli Chapel in the church of Santi Gregorio e Siro, was the first monumental altarpiece painted by Guercino, then aged twenty-nine, for a church in Bologna.

Bearing witness to the importance of the commission is the careful preparation with twenty or so drawings, in which Guercino used all his knowledge, ranging from contemporary Bolognese painting, most notably that of Ludovico Carracci, to the Veneto artists, from the latest Titian to Jacopo Bassano.

On the large canvas, the figures are arranged against a stormy sky in a complex composition.

In the upper part are the Madonna and Child, flanked by two saints and an angel pointing downwards, while in the lower part, St. William, followed by his soldiers and dressed in shining armour, kneels before the bishop to be dubbed with the sword and to receive the cowl or monastic habit.

The scene has a dramatic layout with two lateral backdrops composed of the white robes of the monks to the right, and by the black mass of the bishop’s robe to the left, while the soldiers’ horses against the background appear to break into the foreground.

The painting style with its quick touches of colour and violent juxtaposition of light and shadow, as in the angel's arm that stands out against the dark blue stain of the Madonna's robe, are the most original notes in Guercino's style during these years.

The elaboration of this strong expressive language full of contrasts sanctioned the recognition of the painter as a leader, garnering the admiration of artists and art critics.