I'm guessing that it had to be defined so many times because it has so long been under attack from all quarters.
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That would seem to be the case.
Evidenced at least by the fact that each successive definition was more specific and more detailed.
Compare it to the 3 Creeds of the Church.
The Apostles' Creed seemed to be sufficient at the time.
But then came the heresies. In fact, I've seen the history of the major heresies arranged in chronological order next to the 12 Articles of the Creed and it is a dead ringer, almost as if the Creed was a prophesy of troubles to come.
Then there was the Athanasian Creed, addressing principally the Arian heresy and the denial of the nature of God.
Then came the Nicene Creed which incorporated an abbreviated form of the Athanasian as well as many other details in other topics.
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It scares me to think how much LONGER a new Creed would have to be which puts Modernism into its place -- have a look at the Oath Against Modernism or the Catechism of Modernism by the great Fr. Lemius (no doubt a
genius priest, if not "merely" a saint!).
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In both cases, it wouldn't make sense historically for the third version (?) to have occurred first.
(We don't call subsequent dogmatic definitions "versions" of the first one.)
Then the Apostles, who were simple men, albeit personally infallible, would have had to come up with all the pithy nuances of the Nicene Creed, when it is said that the 12 Articles were each contributed by one each of the 12 Apostles. It would seem you'd need a few more Apostles for stuff like "...Who proceeds from the Father and the Son, and together with the Father and the Son is adored and glorified." Would, "Who spoke to the prophets," have been another article? Or "I believe in One, Holy, Catholic and Apostolic Church..." They would have had to use their own title in "Apostolic" (but they were too humble for that!) -- did they even call each other "Apostles" or the Church "Catholic?" "Hey, Peter, have you seen Bartholomew the Apostle around here lately?"
TLDR...