Saints played a very important role in the popular piety of the late Middle Ages. They were considered to be not only patrons and protectors against all manner of ills, but also mediators between the individual worshiper and God.
In this unusual scene, fourteen saints participate as witnesses at the Baptism of Christ. All the saints are vividly characterized by costume and attributes. They include the giant Christopher carrying the Christ Child on his shoulders, Catherine of Alexandria with sword and wheel of her martyrdom, Augustine holding his heart pierced by the arrow of divine love, Mary Magdalene with her ointment jar, and the chivalrous George kneeling on his dragon. The gold background, the luminescent cloud on which the saints float, and the unrealistic island setting for the Baptism itself all impart a visionary quality to the scene.
The Master of the Saint Bartholomew Altar, named after his monumental altarpiece now in Munich, was active in Cologne. Early in his career he seems to have worked as a manuscript illuminator, and this tradition is evident in his fluid paint handling and sparkling treatment of decorative details.
More information on this painting can be found in the Gallery publication German Paintings of the Fifteenth through Seventeenth Centuries, which is available as a free PDF https://www.nga.gov/content/dam/ngaweb/research/publications/pdfs/german-painting-fifteenth-through-seventeenth-centuries.pdf