What many might not know is that [Brigham] Young is responsible for some of the most unorthodox teachings imaginable. For example, in 1857 he taught that Jesus Christ “was more or less contaminated with fallen nature” and that Christ was “influenced by this nature that we have received” (Journal of Discourses 6:95-96). In 1859, he confessed that his God was “once a man in mortal flesh” (Journal of Discourses 7:333), which had been taught by Joseph Smith in 1844
Young also taught that every person is required to “have the certificate of Joseph Smith, junior, as a passport to their entrance into the mansion where God and Christ are” (Journal of Discourses 7:238. See also Search These Commandments, 1984, p.133)
Unlike the more politically correct LDS Church of today, Young did not hold back in making it clear that those outside his church were not true Christians. In 1863, he insisted that the reason Mormons “differ from other Christians, as they are called, is simply because they [non-Mormons] are not Christians as the New Testament defines Christianity” (Journal of Discourses 10:230)
In fact, he taught that “the Christian world, so-called, are heathens as to their knowledge of the salvation of God” (Journal of Discourses 8:171)
While some would like to dismiss Young’s teachings, he did not allow for that option: “If there is an Elder here, or any member of this Church. . . who can bring up the first idea, the first sentence that I have delivered to the people as counsel that is wrong, I really wish they would do it; but they cannot do it, for the simple reason that I have never given counsel that is wrong; this is the reason” (Journal of Discourses 16:161).
From Mormonism Research Ministry’s “Temple Square Free Visitor’s Guide”