The most convinging theory I've heard was that Revelations was about then-contemporary events, people, and groups, displayed allegorically so the writer wouldn't be beheaded for political dissent or stoned for heresy (there was no "freedom of the press" back then). This trick was also used by Nostradamus and other ancient/medieval writers in times when saying what you meant about those in power was career- or life-threatening.

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort