This highly accomplished monumental work was carved by an unknown sculptor active in northern Germany or Denmark. A sculpture by the same artist, which displays the same voluminous but organized curls in the hair and beard, comes from Tjustrup near Copenhagen (Nationalmuseet, Copenhagen). The sculptor may have been based in Lübeck in northern Germany, which was an important artistic center at this period.
Representations of the Trinity — God the Father, Christ, and the Holy Ghost symbolized by a dove — became popular in northern Europe beginning in the twelfth century. This sculpture depicts the specific theme known as the Seat of Mercy or the Throne of Grace (in German, Gnadenstuhl), in which God the Father holds the body of the crucified Christ on his lap. Here, Christ opens his hand to display his wound, and gestures to his side, as the enthroned God embraces his son.
On the left, Saint Catherine looks at a book and holds the spoke of a wheel, instrument of her martyrdom. At her feet is a tiny figure of Maxentius, her tormentor. On the right, a bishop saint, perhaps Nicholas, makes a sign of benediction. Although now set in a nineteenth-century frame, these figures would have formed the original center section of an altarpiece, probably accompanied by wings with smaller figures.
Source: Alan Chong, "The Trinity with Saint Catherine and a Bishop Saint," in Eye of the Beholder, edited by Alan Chong et al. (Boston: ISGM and Beacon Press, 2003): 31.