The Mass of St. Gregory from the Golden Legend

 

"A woman who sometimes offered bread in the church, as was the usage of the faithful, began one day to laugh when, at the consecration, Gregory uttered the words: 'May the Body of Our Lord Jesus Christ profit thy soul unto life everlasting!' At once the saint drew back the hand which was about to place the Host upon the woman's tongue, and set the sacred Host upon the altar. Then, before all the congregation, he asked the woman why she had dared to laugh. And the woman made answer: 'I laughed because you called this morsel of bread, which I kneaded with my own hands, the "Body of Christ."' Then Gregory prostrated himself and prayed to God for the woman's unbelief; and when he arose, he saw that the Host which lay upon the altar had changed into a piece of flesh in the form of a finger. He showed this flesh to the incredulous woman, who immediately came back to the faith. And again the saint prayed, and again the flesh took the form of bread; and Gregory gave it in Communion to the woman."

The Mass of St. Gregory establishes the theme of acceptance and rejection of Christ as central to the meaning of the altarpiece.