Why do some historians believe Byzantine art included government propaganda

Byzantine art referred to the artistic product of Byzantium, which was part of the Eastern Roman Empire. The Byzantine Empire remained intact even after the fall of the Western Roman Empire up until the declined of Constantinople in 1453. Historians believed that many eastern orthodox states and some Muslim states in the east Mediterranean had been influenced by Byzantium's art and culture, and had preserved some aspects of Byzantine arts for centuries.

I'm not really sure this is what I know