Rev 22:18 - For I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto these things, God shall add unto him the plagues that are written in this book: ...
I think this is fairly straight forward. As is required throughout the entire collection of Scripture God intended this book to be read and interpreted in the literal sense except for when figures of speech such as metaphors, similies, types, etc., are obviously what's in view.
Verse 18, which is unique to every other book in the Bible, compliments the other uniqueness of the book in Rev. 1:3, where God promises a special blessing on those who, "readeth, and they that hear the words of this prophecy, and keep those things which are written therein: ..."
IOW, those who read and understand this book of God's plan for the future of mankind are promised a blessing. But if readers are confounded, confused and misled by the mis-interpretations of those who add or take away from the book by spiritualizing or allegorizing large parts of it then that blessing will not be realized by the reader.
There's a reason why God placed so much importance on the preservation of his original intent in this book, and why judgment will come down so hard on those who corrupt that meaning with their mis-interpretations. These two verses, like bookends to the book, are the only places in Scripture that promise a blessing and a curse to those who read it. That's how important it is to God that readers get it right.
As to the Catholic Church being Babylon ... I'm only speaking from memory, and am certainly not a Babylon guru, but didn't the reformers emphasize only that the Pope was antichrist? I don't recall mention of them saying the Roman church was Babylon. I could easily be wrong.
