Zweiseitiges Altarbild: Vorderseite (jeweils zwei Teile), Ausgießung des Heiligen Geistes, Hinterseite, Gregors Messe

Jan Wellens de Cock was an Antwerp painter active in the early sixteenth century, associated with the circle of Hieronymus Bosch and the generation that absorbed Bosch's fantastic imagery into the mainstream of Antwerp panel painting. This double-sided altarpiece, with the Pentecost and the Mass of Saint Gregory on its respective faces, represents the standard devotional double function of Flemish altarpieces where both interior and exterior surfaces carried sacred content. The Mass of Saint Gregory — a miraculous apparition of Christ to Pope Gregory — was one of the most popular devotional subjects in early sixteenth-century Flemish painting.

De Cock's Pentecostal composition follows the standard iconography of the descending Holy Spirit in flame above the assembled apostles, with Mary at the centre. The Mass of Gregory on the reverse depicts the altar vision with careful attention to the liturgical setting. The Boschian influence is visible in the fantastic figures and dense compositional organisation that characterises his generation.