2 Nephi 18

Isaiah asked -

"...should not a people seek unto their God for the living to hear from the dead?
20 To the law and to the testimony..." (Book of Mormon 2 Nephi 18:19 - 20)

Much of the instruction we find in the scriptures, of which much is quoted in modern-day gospel counsel and instruction is the law and testimony given by the dead. The dead are prophets that have testified concerning their dealings with God. Paul reminds us -

"...In the mouth of two or three witnesses shall every word be established." (New Testament 2 Corinthians 13:1)

Nephi understood this as he testified of the Savior -

"And now I, Nephi, write more of the words of Isaiah, for my soul delighteth in his words. For I will liken his words unto my people, and I will send them forth unto all my children, for he verily saw my Redeemer, even as I have seen him.
3 And my brother, Jacob, also has seen him as I have seen him; wherefore, I will send their words forth unto my children to prove unto them that my words are true. Wherefore, by the words of three, God hath said, I will establish my word. Nevertheless, God sendeth more witnesses, and he proveth all his words." (Book of Mormon 2 Nephi 11:2 - 3)

It is testimonies such as this that Isaiah prophecies of speaking of scattered Israel -

"And thou shalt be brought down, and shalt speak out of the ground, and thy speech shall be low out of the dust, and thy voice shall be, as of one that hath a familiar spirit, out of the ground, and thy speech shall whisper out of the dust." (Old Testament Isaiah 29:4)

Speaking of the writings of his people, Nephi writes -

"For those who shall be destroyed shall speak unto them out of the ground, and their speech shall be low out of the dust, and their voice shall be as one that hath a familiar spirit; for the Lord God will give unto him power, that he may whisper concerning them, even as it were out of the ground; and their speech shall whisper out of the dust." (Book of Mormon 2 Nephi 26:16)

Moroni in his closing remarks writes -

"I exhort you to remember these things; for the time speedily cometh that ye shall know that I lie not, for ye shall see me at the bar of God; and the Lord God will say unto you: Did I not declare my words unto you, which were written by this man, like as one crying from the dead, yea, even as one speaking out of the dust?" (Book of Mormon Moroni 10:27)

One of those records that we hear from the dead is the Book of Mormon. In the introduction we read -

"The ancient record thus brought forth from the earth as the voice of a people speaking from the dust, and translated into modern speech by the gift and power of God as attested by Divine affirmation, was first published to the world in the year 1830 as THE BOOK OF MORMON." (Book of Mormon Preface Joseph Smith:25)