Why was this made, and how was it used?
The Morgan Bible is believed to have been made as a political statement under the crusader King Louis IX of France. The Franks, under the command of Louis IX, viewed themselves as the rightful descendants of the Old Testament heroes shown in this manuscript. They viewed their engagement in battles in the Holy Land as connected to the battles in the Holy Land fought by the Israelites. King Louis IX also used his role in the crusades to legitimize his reign at home.
In general, Christian Bibles in the Middle Ages were used to present the teachings of Christianity. Illustrated, or illuminated, Bibles could be used by monks and other missionaries to spread Christianity in the years before widespread literacy. However, the size and luxury of this illuminated manuscript suggest elite patronage. An illuminated manuscript of this size and luxury would require high intellectual, artistic, and financial resources.
When the Morgan Bible was first made, it contained only images, without any text. (The texts you see on the folio were added later.) The initial lack of text meant that the audience of this manuscript needed to be knowledgeable about the Old Testament, otherwise they would not be able to recognize the characters and events on the folio.