What contrast is Dunstan aware of between the “kneeling petitioners” and “art lovers” (201)?

From the text:

The picture was not my chief concern, however. My eyes were on the kneeling petitioners, whose faces had the beauty virtually every face reveals in the presence of the goddess of mercy, the Holy Mother, the figure of divine compassion. Very different, these, from the squinnying, lip-biting, calculating faces of the art lovers one sees looking at Madonnas in galleries.