The Latin word credo means simply "I believe." It represents the first word of the Apostles' Creed. Throughout church history it has been necessary for the church to adopt and embrace creedal statements to clarify the Christian faith and to distinguish true content from error and false representations of the faith. Such creeds are distinguished from Scripture in that Scripture is norma Normans ("the rule that rules"), while the creeds are norma normata ("a rule that is ruled").
Historically, Christian creeds have included everything from brief affirmations to comprehensive statements. The earliest Christian creed is found in the New Testament, which declares, "Jesus is Lord." The New Testament makes a somewhat cryptic statement about this affirmation, namely, that no one can make the statement except by the Holy Spirit. What are we to understand by this? On the one hand, the New Testament tells us that people can honor God with their lips while their hearts are far from Him. That is to say, people can recite creeds and make definitive affirmations of faith without truly believing those affirmations. So, then, why would the New Testament say that no one can make this confession save by the Holy Spirit? Perhaps it was because of the cost associated with making that creedal statement in the context of ancient Rome.
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.
The creeds also used that summary content to exclude the heretics of the fourth century. In the affirmation of the Nicene Creed, the church affirmed categorically its belief in the deity of Christ and in the doctrine of the Trinity. These affirmations were seen as essential truths of the Christian faith. They were essential because without inclusion of these truths, any claim to Christianity would be considered a false claim.
Taken from "Norma Normata: A Rule that is Ruled" (used by permission).