Thou shalt not add to, subtract from, or change the words of Scripture. Mormons have a second Bible, the Book of Mormon. They also have an armful of other books and revelations to change any doctrines they find inconvenient (like the doctrine of polygamy a century ago, or racism today). Against such ``revelations'' the Bible stations four watchdogs:
Dt. 4:2. Don't add anything to what I order you to do or take anything away from it, but keep the commandments of the Lord your God that I order you to keep. (AAT)
Dt. 12:32. Be careful to do everything I order without adding to it or taking anything from it.
Pr. 30:5-6. Everything God said has proved to be true. He's a Shield to those who come to Him for protection. Don't add anything to what he says or He will correct you, and you will be found a liar.
Rv. 22:18-19. I warn everyone who hears what the prophecy of this book tells him: If you add anything to this, God will add to you the plagues written in this book. And if you take away any words in this book of prophecy, God will take away your share in the tree of life and in the holy city that are described in this book.
The Revelation passage above does not mean that taking one word out of Scripture is a particularly damnable sin, just that people who start out by fiddling with the Scriptures always end up cutting out the Gospel of Christ. The Bible is a seamless garment, and just as one hole in a pair of pantyhose means they are as good as rags, so the slightest deletion from Scripture turns that sacred Book into ``holy rags.'' The Gospel of Christ will eventually be taken out. Without him we are lost. I once had an old parishioner who denied a single Scripture. I went to him with an old Bible and a pair of scissors. I cut the offending passage out but then proceeded to cut out everything implied by the offending passage. Then I offered him the Bible. Funny, he didn't want it. Neither did I.
Some cultists claim their second Bibles are just another Testament. Very interesting! An unpredicted Testament that contradicts everything in both Old and New!