Final answer:
The form and decor of Justinian's Hagia Sophia and San Vitale in Ravenna reinforce the idea of Christian imperium and the emperor's role as guarantor of Christian concord.
Step-by-step explanation:
The form and decor of Justinian's Hagia Sophia and San Vitale in Ravenna are reflective of the idea of Christian imperium and the emperor's role as guarantor of Christian concord.
Both churches were built during the reign of Justinian I, who displayed his piety by funding the construction of churches and participating in religious rituals.
The architecture and artwork of these churches, such as mosaics depicting emperors and empresses, Greek iconography, and the lavish use of gold, symbolize the emperor's power and the divine nature of Christianity.