As a missionary many non members made the ridiculous claim that these verses are John telling us there is to be no more revelation.
Revelation 22:18 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.
Interestingly, these verses are not as unique as they believed, as Moses declared:
Deuteronomy 4:2 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.
Adding to the irony, those who were offended by additional revelation were generally the same crowd that said John 3:16 is "all you need". That is, they were upset about new revelation, but believed there was no harm in discarding all but a single verse of the scriptures.
The Lord's description of such people is spot on.
2 Nephi 29:6 Thou fool, that shall say: A Bible, we have got a Bible, and we need no more Bible. Have ye obtained a Bible save it were by the Jews?
7 Know ye not that there are more nations than one? Know ye not that I, the Lord your God, have created all men, and that I remember those who are upon the isles of the sea; and that I rule in the heavens above and in the earth beneath; and I bring forth my word unto the children of men, yea, even upon all the nations of the earth?
8 Wherefore murmur ye, because that ye shall receive more of my word? Know ye not that the testimony of two nations is a witness unto you that I am God, that I remember one nation like unto another? Wherefore, I speak the same words unto one nation like unto another. And when the two nations shall run together the testimony of the two nations shall run together also.
9 And I do this that I may prove unto many that I am the same yesterday, today, and forever; and that I speak forth my words according to mine own pleasure. And because that I have spoken one word ye need not suppose that I cannot speak another; for my work is not yet finished; neither shall it be until the end of man, neither from that time henceforth and forever.
10 Wherefore, because that ye have a Bible ye need not suppose that it contains all my words; neither need ye suppose that I have not caused more to be written.
11 For I command all men, both in the east and in the west, and in the north, and in the south, and in the islands of the sea, that they shall write the words which I speak unto them; for out of the books which shall be written I will judge the world, every man according to their works, according to that which is written.