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.
I can’t help but think of Nephi’s vision here. People did take away and add to the Bible, and to his prophecy specifically. I’m thinking of 1 Nephi 14:23, but also Ether 4:15-16:
15 …yea, when ye shall call upon the Father in my name, with a broken heart and a contrite spirit, then shall ye know that the Father hath remembered the covenant which he made unto your fathers, O house of Israel.
16 And then shall my revelations which I have caused to be written by my servant John be unfolded in the eyes of all the people. Remember, when ye see these things, ye shall know that the time is at hand that they shall be made manifest in very deed.
As Nephi said back in his vision, a huge part of what is obscured by the “Great and Abominable Church” is the Abrahamic Covenant. And here Moroni says that when the House of Israel remembers God and realizes that God remembers their ancient covenant, then the revelations which John wrote will make sense!
I think it’s also why Isaiah doesn’t make sense to most people.
I find it interesting that Nephi (in 1 Nephi 13) says that first, “they have taken away from the gospel of the Lamb many parts which are plain and most precious; and also many covenants of the Lord have they taken away.” Then second, “that there are many plain and precious things taken away from the book, which is the book of the Lamb of God.” What I gather is that first, there were things that became unnecessary to a certain way of teaching the gospel, so eventually they were removed from the book because they no longer made any sense. The obvious example would be the Abrahamic Covenant. If the gospel was being mostly preached to Gentiles, then of what use was that ancient covenant? It became associated with the Law of Moses, which was clearly done at the time of Christ’s coming. So goes the Abrahamic Covenant, and God’s future work with Israel (and especially the Jews, from most people in history’s perspective).
Note that this wasn’t done completely innocently: “And all this have they done that they might pervert the right ways of the Lord, that they might blind the eyes and harden the hearts of the children of men.” But you can see how the Gentiles who received this teaching and this book took it innocently. Nephi describes them as “stumbling” because they don’t have understanding. And of course so the Book of Mormon comes along to help restore this understanding of the gospel so that when we read the Bible, we can see that the ancient covenant is still at work and that priesthood still has a saving and sealing power as it once did. And many other plain and precious things, too.
Anyway, I know that the verses from Revelation that I originally quoted have been used against Mormons to say that the Book of Mormon is evil because it adds to the Bible. But it seems clear to me that John is warning against taking from or adding to his own prophecy, which is exactly what Nephi saw happening. And the Book of Mormons’ purpose is precisely to point people to the Bible. As Nephi puts it:
…convincing of the Gentiles and the remnant of the seed of my brethren, and also the Jews who were scattered upon all the face of the earth, that the records of the prophets and of the twelve apostles of the Lamb are true.
And the angel spake unto me, saying: These last records,which thou hast seen among the Gentiles, shall establish the truth of the first, which are of the twelve apostles of the Lamb.