The keystone of the Mormon Church is the Book of Mormon. When I first read it, something that stood out to me (apart from the anachronistic appearance of Deutero–Isaiah) was the question of why it didn’t mention key parts of Joseph Smith′s restoration of the gospel (e.g., polygamy, the ordinances of the temple, and the restored priesthood). However, I’ve come to realize that when Joseph Smith penned the Book of Mormon he was more interested in answering some theological disputes that were floating around in that time period, notably, that of the Native Americans as Israelites, proper baptism practices, and the relationship between works and grace.
Smith also used the Book of Mormon to sacralize America, an idea which I don’t think was that uncommon in nineteenth-century America, with other religious figures and movements also portraying America as being a sacred land that has a sacred history and a divine destiny. This can be seen in how the Book of Mormon refers to the Americas as the “land which is choice above all other lands” (1 Nephi 2:20). In fact, the Book of Mormon takes such sacralizing thinking further, providing the reader with what is essentially an American-based history of antiquity. On top of this, you have Joseph Smith teaching that not only was the United States the site of the Garden of Eden (somewhere around Jackson County, Missouri), but it was also the location of the Zion/New Jerusalem (he was given a revelation that Zion would be built in Independence, Missouri, see Doctrine and Covenants 57:1-3).
Personally, I think Joseph Smith’s theological agenda was quite flexible and what was really important to him was his vision of the making of Zion with himself as its leader. He did, after all, have ambition that seemingly held no bounds, such as running as a candidate for the President of the United States in 1844. Additionally, a Council of Fifty was formed in order to develop a world government in preparation for Christ’s return, with Smith being anointed king over the House of Israel.
It was through Joseph Smith that Zion was to be established in the last days for humanity’s salvation. In the pursuit of this goal, Joseph Smith and his followers attempt three times to establish what can only be described as their own city-state, first in Kirtland, Ohio, then in Independence, Missouri, and finally in Nauvoo, Illinois. The Mormons thrived in Nauvoo, leading to a Nauvoo legion being formed (consisting of about 5,000 members at its peak), led by the “Lieutenant General” Joseph Smith. Smith′s successor, Brigham Young, was responsible for the most successful attempt of building Zion to date (or, at least, a type of precursor to Zion), leading many of the Mormons westward to Utah, founding Salt Lake City in the late 1840s.
One last thought: In 2015, the Mormon Church released photos of the seer stone that Joseph Smith used in his “translation” of the Book of Mormon (see this article). While the idea that Joseph Smith put his head into a hat containing this stone in order to translate the golden plates (containing the Book of Mormon) may seem quite bizarre, I don’t think it is necessarily so. I mean, the Hebrew Bible has people receiving divine revelations through something that resembles a game of chance (the Urim and Thummin), and even through a fleece of wool being laid out on a threshing floor to see if it gets covered in dew. I think non-Mormon Christians only find Smith′s stone-in-a-hat method weird because it seems like folk-magic (with no biblical pedigree), while something equally bizarre like the Urim and Thummin gets a pass simply because it is in the Bible.
I think it is good that the Mormon Church has taken this turn of transparency. Perhaps it will mean the coming generations of Mormons will grow up with less of this type of picture …