Someone has mentioned this to me. Astonishing.
Although, as I admit, it is hard to make out in this small web version of the original masterpiece, the painting shows the Virgin Mary in the sky, bestowing upon St Ildefonso, the 7th century bishop of Toledo, a vestment for the celebration of the Eucharist. Saint Ildefonso, the patron saint of Toledo, was a great scholar and theologian; he wrote, among many other things, the Liber Prosopopoeia Imbecillitatis Propriae, the proposition on his own imbecility. They don’t make them like they used to.