In order to facilitate these changes, the Mormon Church introduced the believe in 'continuing revelation.' History shows that the god of Mormonism frequently changes his mind, often contradicting his earlier revelations. This tends to happen whenever doing so is convenient to the Mormon Church. (On this, see The Changing World of Mormonism; an online book).
Fundamentalist Mormons hold to the foundational (fundamental) teachings on which Mormonism was original built.
...LDS Church authorities bristle visibly when Mormons and Mormon Fundementalists are even mentioned in the same breath. As Gordon B. Hinkley, the then eighty-eight-year-old LDS president and prophet, emphasized during a 1998 television interview with on
Larry King Live,
"They have no connection with us whatsoever. They don't belong to the church. There are actually no Mormon Fundementalists."
Nevertheless, Mormons and those who call themselves Mormon Fundamentalists (or FLDS) believe in the same holy texts and the same sacred history. Both believe that Joseph Smith, who founded Mormonism in 1830, played a vital role in God's plan for mankind; both LDS and FLDS consider him to be a prophet comparable in stature to Moses and Isaiah.
Mormons and Mormon Fundamentalists are each convinced that God regards them, and them alone, as his favored children: "a peculiar treasure unto me above all people."
But if both proudly refer to themselves at the Lord's chosen, they diverge on one especially inflamatory point of religious doctrine: unlike their present-day Mormon compatriots, Mormon Fundamentalists passionately believe that Saints have a divine obligation to take multiple wives. Followers of the FLDS engage in polygamy, they explain, as a matter of religious duty.
[...]
The LDS Church happens to be exceedingly prickly about its short, uncommonly rich history - and no aspect of that history makes the church more defensive than "plural marriage."
The LDS leadership has worked hard to persuade both the modern church membership and the American public that polygamy was a quaint, long-abandoned idiosyncrasy practiced by a mere handful of nineteenth-century Mormons.
The religious literature handed out by the earnest young missionaries in Temple Square makes no mention of the fact that Joseph Smith - still the religion's focal personage - married at least thirty-three women, and probably as many as forty-eight. Nor does it mention that the youngest of these wives was just fourteen years old when Joseph explained to her that God had commanded that she marry him or face eternal damnation.
Polygamy was, in fact, one of the most sacred credos of Joseph's church - a tenet important enough to be canonized for the ages as Section 132 of
The Doctrine and Convenants, on of Mormonism's primary scriptural texts.
Source: Fundamentalist vs. mainstream LDS doctrine on polygamy, Brooke Adams, The Salt Lake Tribune, Mar. 14, 2004