how do you figure, we didn't add another book to the gospel.
Where does this "WE" come from?
Did you write the New Testiment?
The original Bible or Torah was the first several chapters of the Old Testiment. Then the New Testiment was added and other chapters added to the Old Testiment.
Jews could claim "YOU" added another book to their book.
Revelation 22:18-19
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:
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.
What is God saying here?
You do not have to be a genius to understand these words. God says: “This is the End. Don’t tamper with it. The Word of God is now complete. No more messages from God are to be expected. This is the last message from God to the last of the Apostles just before he died. No more prophecies from God will be added.”
Paraphrased God says very plainly in Revelation 22:18, “If anyone comes to you claiming that he or she has a new message from God, which has come to that person in a dream, or in a vision, or in an angel visitation, or in a tongue, or even if not a word was spoken but that person saw a comforting light somewhere in the middle of the night, or saw any other supernatural manifestation from God, then know that this person is lying, for God will not give any more Divine revelations or messages; that person is a false prophet, and I have not send them, and he or she deserves to be tormented in the Lake of Fire, so that the smoke of their torment ascendeth up forever and ever”.
Therefore if anyone comes to you claiming that he or she has a new message from God, that person has added to the Word of God, the Bible, for the Bible is this One Book that God mentions in Revelation 22:18.
Here, on the last page of the Bible, God gave a last warning that the Bible is now complete; no one should add words to it, and neither will God add any more words to it. We must realize that the Bible portrays the image of God, and whosoever has additional Divine revelations has added to the words of the Bible, and is guilty of tampering with the image of God. Moreover, if any man shall take away from the words of the Book of this prophecy, God shall deny him entrance to the New Jerusalem, for he or she has also tampered with the image of God