Revelation 22:18,19

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:

19 And if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life, and out of the holy city, and from the things which are written in this book.

God takes the prophetic message He gave to John seriously. Any who add to the words of this prophecy will receive the plagues written in this book and those that take away the words of this prophecy will be cast into the Lake of Fire. That warning has kept many from tampering with the text but it probably has a deeper prophetic meaning as well.

Those who say they understand the words and then spiritualize or allegorize them to mean something other than what was said may miss the Rapture and go through the tribulation (The plagues in this book -- i.e. the theologians in Thyatira, Sardis and Laodicea). Those who say these scriptures are not even God's word do not have any part in the promises in this book. They will be cast into the Lake of Fire.