The "kingdom" of God and "gospel" are usually thought of as terms unique to Christianity. And who else but Jesus was called not only "the son of God" but also "Lord" and "Savior"? In fact, say biblical experts, these terms and concepts were already familiar to residents of the Roman Empire who knew them as references to the authority and divinity of the emperors, beginning notably with Caesar Augustus before the dawn of the first century.

Julius Caesar was assassinated on the Ides of March in 44 BC. When a comet was later visible on July nights, Octavius, the adopted son and heir of Julius Caesar, promoted the idea that it was a sign that the divine Caesar was on his way to heaven. When Roman law in 42 BC deified Julius Caesar, the status of Octavius, who took the name Augustus, was strengthened by adding the phrase "son of God." Poets celebrated the divinity associated with Augustus, and across the empire coins, monuments, temples and artwork promoted the cult of Augustus and other emperors who adopted Caesar as an honorific title. To many in the empire, Roman civilization brought stability and wealth. And the people were urged to have "faith" in their "Lord," the emperor, who would preserve peace and increase wealth. "In the Roman imperial world, the 'gospel' was the good news of Caesar's having established peace and security for the world," wrote Richard A. Horsley in Jesus and Empire.

Christians gave secular words associated with the empire a new meaning. The Greek word parousia referred to the triumphant arrivals of emperors into cities. In churches it meant the expected return, or second coming, of the heavenly exalted Christ. Churches, literally "assemblies," were the Christian counterparts to the Roman ekklesiai where Caesar was celebrated, according to Horsley, a professor at the University of Massachusetts at Boston. "Caesar was the 'Savior' who had brought 'salvation' to the whole world."

In that context, the Christmas passage in the Gospel of Luke has a subversive tone, says Horsley. Angels bring "good news" of joy "to all the people," because of the birth of a "Savior, who is the Messiah, the Lord." A heavenly multitude joins the angels in proclaiming "on earth peace among those whom he favors." For the Romans, peace was the militarily imposed Pax Romana, and it was already guaranteed by Rome.