A very good explanation of this subject is contained in 2 Nephi, chapter 3. Lehi was rehearsing to his son Joseph, some important promises which the Lord made to their father, Joseph, who was sold into Egypt. The special promise to which we refer is in the twelfth verse.
"Wherefore, the fruit of thy loins shall write; and the fruit of the loins of Judah shall write; and that which shall be written by the fruit of thy loins, and also that which shall be written by the fruit of the loins of Judah, shall grow together, unto the confounding of false doctrines, and laying down of contentions, and establishing peace among the fruit of thy loins, and bringing them to the knowledge of their fathers in the latter-days; and also to the knowledge of my covenants, saith the Lord."
The following from the writings of O. Pratt, is very appropriate to this subject.
"If the historical parts of the Book of Mormon be compared with what little is known from other sources, concerning the history of ancient America, there will be found much evidence to substantiate its truth; but there cannot be found one truth among all the gleanings of antiquity that clashes with the historical truths of the Book of Mormon.
"If the prophetical part of this wonderful book be compared with the prophetical declarations of the Bible, there will be found much evidence in the latter to establish the truth of the former. But though there are many predictions in the Book of Mormon, relating to the great events of the last days, which the Bible gives us no information about, yet there is nothing in the predictions of the Bible that contradicts in the least, the predictions of the Book of Mormon.
"If the doctrinal part of the Book of Mormon be compared with the doctrines of the Bible, there will be found the same perfect harmony which we find on the comparison of the prophetical parts of the two books. Although there are many points of the doctrine of Christ that are far more plain and definite in the Book of Mormon than in the Bible, and many things revealed in relation to doctrine that never could be fully learned from the Bible, yet there are not any items of doctrine in the two sacred books that contradict each other, or clash in the least.
"If the various books which enter into the collection, called the Book of Mormon, be carefully compared with each other, there will be found nothing contradictory in history, in prophecy, or in doctrine.
"If the miracles of the Book of Mormon be compared with the miracles of the Bible, there cannot be found in the former anything that would be more difficult to believe, than what we find in the latter.
"If we compare the historical, prophetical, and doctrinal parts of the Book of Mormon, with the great truths of science and nature, we find no contradictions—no absurdities—nothing unreasonable. The most perfect harmony, therefore, exists between the great truths revealed in the Book of Mormon, and all other known truths, whether religious, historical, or scientific." Divine Authenticity of B. of M., page 56.
A person educated in the doctrines and traditions of modern Christianity, could not have written the Book of Mormon, for many of its important doctrines do not agree with those of the Christian sects.