Preserved by the Hand of God

And I, Mormon, pray to God that they may be preserved from this time henceforth. And I know that they will be preserved; for there are great things written upon them, out of which my people and their brethren shall be judged at the great and last day, according to the word of God which is written. - Words of Mormon 1:11

And for this very purpose are these plates preserved, which contain these records—that the promises of the Lord might be fulfilled, which he made to his people. - Doctrine and Covenants 3:19