"The loyalty oath required by Roman citizens to demonstrate their allegiance to the empire in general and to the emperor in particular was to say publicly, “Kaisar Kurios,” that is, “Caesar is lord.” In the first-century church, Christians bent over backward to be obedient to civil magistrates, including the oppressive measures of Caesar, and yet, when it came to making the public affirmation that Caesar is lord, Christians could not do so in good conscience. As a substitute for the phrase, “Caesar is lord,” the early Christians made their affirmation by saying, “Jesus is Lord.” To do that was to provoke the wrath of the Roman government, and in many cases, it cost the Christian his life. Therefore, people tended not to make that public affirmation unless they were moved by the Holy Spirit to do so. The simple creed, “Jesus is Lord,” or more full statements, such as the Apostles’ Creed give an outline of basic, essential teachings. The creeds summarize New Testament content."
~R.C. Sproul