The biblical text is corrupted and therefore is insufficient to communicate a message of salvation, apart from the interpretive authority of the Book of Mormon — necessitating extra-biblical inscripturated revelation.
(I Nephi 13: 24-29) “And the angel of the Lord said unto me: Thou hast beheld that the book proceeded forth from the mouth of a Jew; and when it proceeded forth from the mouth of a Jew it contained the fulness of the gospel of the Lord … Wherefore, these things go forth from the Jews in purity unto the Gentiles, according to the truth which is in God. And after they go forth by the hand of the twelve apostles of the Lamb, from the Jews unto the Gentiles, thou seest the formation of that great and abominable church, which is most abominable above all other churches; for behold, 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. 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. Wherefore, thou seest that after the book hath gone forth through the hands of the great and abominable church, that there are many plain and precious things taken away from the book, which is the book of the Lamb of God … because of these things which are taken away out of the gospel of the Lamb, an exceedingly great many do stumble, yea, insomuch that Satan hath great power over them.”
(II Nephi 29:3, 6) “And because my words shall hiss forth—many of the Gentiles shall say: A Bible! A Bible! We have got a Bible, and there cannot be any more Bible … 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?”
Not only is the Bible insufficient for salvation, but the Book of Mormon threatens eternal condemnation to those who reject it.
(Book of Mormon Title Page, 1830) “Wherefore, it is an abridgment of the record of the people of Nephi, and also of the Lamanites … And now, if there are faults they are the mistakes of men; wherefore, condemn not the things of God, that ye may be found spotless at the judgment-seat of Christ.”
(Mormon 8:12, 17) “And whoso receiveth this record, and shall not condemn it because of the imperfections which are in it, the same shall know of greater things than these … And if there be a faults they be the faults of a man. But behold, we know no fault; nevertheless God knoweth all things; therefore, he that condemneth, let him be aware lest he shall be in danger of hell fire.”
(Ether 12:25-26) “When we write we behold our weakness, and stumble because of the placing of our words; and I fear lest the Gentiles shall mock at our words. And when I had said this, the Lord spake unto me, saying: Fools mock, but they shall mourn.”