The Angels who surround the enthroned Christ have an interesting quality. Prior to this work, all the images of Christ figure have him surrounded by apostles (old men) and / or historic figures (more old men).
Here we see a palace guard. These are virile young men flashing gang signs while holding the Byzantine equivalent of clubs who are hanging out in front of the throne. They shake down the virgins and kings on one side, and the command an army martyrs on the other side.
You're god, for what reason do you need a guard? From whom do you need protection? This interesting transition in the art, the appearance of the palace protection provides a glimpse into the attitudes of the ruling class.
Although we see a Byzantine mosaic, it's likely a interpretation of a previous Ostrogoth concept. The gold sky versus the blue one, the heavenly and earthly sky.