Moroni began is concluding chapter with the exhortation. He then moved to a discussion of the gifts of the spirit, among which was implied the gift of the Book of Mormon and the gift of understanding that it is true based on faith. As part of his prophetic sealing on the plates, he pronounces the wo-statements. He now moves to the final aspect of the seal, which is the testimony. Moroni seals this entire work with his personal testimony that it is true. He notes that he stands as witness of the truthfulness not of the translation, not of the plates, but of the content of the plates. He testifies that the meaning is true, and that he will be the sure witness of that truthfulness when we stand before the judgment bar of God when all of God’s truths will be evident.
[like as one crying from the dead, yea, even as one speaking out of the dust?]: Nephi used a similar benediction at the end of his writing:
2 Nephi 33:13
13 And now, my beloved brethren, all those who are of the house of Israel, and all ye ends of the earth, I speak unto you as the voice of one crying from the dust: Farewell until that great day shall come.
For both Nephi and Moroni, they are witnesses from the dust because their words survive them. They speak to us in the modern day even though their day is long past. While this is the specific usage we see in both Nephi and Moroni, we should understand that the phraseology comes from Isaiah:
Isaiah 29:4
4 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.
Nephi’s obvious mastery of Isaiah tells us that his reference to Isaiah was intentional, and probably seen as a fulfillment of Isaiah’s prophecy. We are less certain of Moroni’s understanding of the ultimate source of this text. However, the presence of the next verse will suggest that Moroni’s immediate reference is Nephi, not Isaiah.