In the daily life of ancient Rome the catchword, "Christ is Lord," was not the pious phrase it seems to be today. It was a battle cry and a subversive one. "Christ is Lord" used the very basis on which the imperium was built, the term kyrios-dominus, and applied it to Christ. Any committee of un-Roman activities would have been emotionally aroused by it. Diocletian was lord, and not the Christian god. That is, Rome would not have minded at all if the phrase had been used in the normal syncretistic framework of cult and mystery, within a pantheon that harmed no one. There you could talk about the "Lord Jesus" as long as it had nothing to do with reality. But for third- and fourth-century man it was a matter of whether or not to place a libation on an altar of a state temple as an act of supreme loyalty to the empire. We understand the explosive character of such early Christian phrases only if we take them out of the familiar context of our contemporary theology and liturgy and try to imagine them as they sounded in antiquity, as concrete and often dangerous phrases inimical to the ears of politicians, priests, and soldiers properly educated in Roman ideology.
from page 34, The Serpent and the Dove