How can one believe the Book of Mormon to be scripture when the Bible says we shouldn't add to the Bible (Revelation 22:18-19)?
The phrases "the prophecy of this book," "the book of this prophecy,"
and "this book" refer only to the book of Revelation. At the time
John recorded those words, the Bible did not exist; there were only separate scrolls
for each book. The first bound Bibles do not appear until the fourth century A.D.
Some of the earliest Bible manuscripts do not end with the book of Revelation
and, in fact, some of them don't even include that book and omit other New
Testament books as well.
Moreover, similar warnings are found in earlier Bible books. For example, in
Deuteronomy 4:2, we read, "Ye shall not add unto the word which I command
you, neither shall ye diminish ought from it, that ye may keep the commandments
of the Lord your God which I command you" (see also Deuteronomy 12:12).
While mortals are forbidden to add to the divine word, the Lord himself is not
bound by such restrictions. God's word is revealed through prophets, and
it is through prophets that he has always added to his own word. Thus, we read
that, when the king had burned the words written by Jeremiah (Jeremiah 36:1-4,
23), the Lord commanded him to restore these words (Jeremiah 36:27-28). "Then
took Jeremiah another roll, and gave it to Baruch the scribe, the son of Neriah;
who wrote therein from the mouth of Jeremiah all the words of the book which
Jehoiakim king of Judah had burned in the fire: and there were added besides
unto them many like words" (Jeremiah 36:32).