The Church of Jesus Christ of Latter-Day Saints, commonly called the Mormons after their Book of Mormon, is today a vast empire of unimaginable wealth and power, centered in Salt Lake City, Utah. But it all started with the revelation of just one man by the name of Joseph Smith in the 1800’s. He claimed to have a visitation from an angel of light.
He then went on to put forth as new divine revelation several books: The Book of Mormon (whose authorship is in question), the Doctrine and Covenants and the Pearl of Great Price. There are several places where the Doctrine and Covenants and Pearl of Great Price seem to outright contradict the Book of Mormon, however.
It has been suggested that the Book of Mormon was originally written by a retired preacher named Solomon Spalding as fiction styled after the Bible, and I suspect that may be accurate, especially since the theology of the Book of Mormon seems to follow the Bible, while the theology of the other books begins to depart significantly. You can read more into that theory here:
Smith claimed that these were additional revelations of Jesus Christ. The problem is, these books make outlandish and utterly bizarre statements and wind up grossly contradicting the Bible. So while he may well have had a vision of an angel of light, we must always keep in mind that, as the Bible warns, even Satan can appear as an angel of light. We must test all things in accordance with the scriptures.
One thing that the average reader will notice right off the bat when approaching the Mormon scriptures is this: they are all in King James-style English. Since obviously by the 1800’s in America people were not speaking in that manner normally, and since Joseph Smith claimed these books were inspired by God, a rather strange and absurd conclusion seems to follow: the God of Mormonism actually speaks King James English. But no, a more rational conclusion is that Joseph Smith copied the style of the King James Bible in order to lend more credibility to his false books by making them sound more like the Bible of their day. The gullible people who followed him fell for it. Actually it can be clearly demonstrated in many places that the various Mormon scriptures actually copied straight out of the King James Bible.
It would be unnecessarily time-consuming to attempt to list out every errant doctrine of the Mormon church here; it’s been done elsewhere anyway. The main problem with their teachings is that they say men and women can become gods and goddesses, and that the God of the Bible is actually just another man from a different planet who eventually succeeded in becoming exalted to godhood himself. They are polytheistic in the most extreme sense; they basically believe in an infinite number of gods. Anyone with a good grasp on the Bible will instantly understand that is pure heresy, and is actually a restatement of Satan’s lie in the Garden of Eden.
Be advised: Mormon door-to-door missionaries are trained to misrepresent their own beliefs to outsiders. They may try to deny that they believe in many gods and that people can become gods. For that, I can recommend if you’re really serious about witnessing to Mormons to get a copy of the Triple Combination (Book of Mormon, Doctrine and Covenants and Pearl of Great Price) and then you can point to them in their own scriptures where it says it.