This is a hard doctrine, one from which too many Latter-day Saints tend to flee. It is the doctrine that Lehi taught (see 1 Nephi 10:4-6), that Benjamin declared (see Mosiah 3:18-19), that Abinadi made known (see Mosiah 16:1-3). that the Brother of Jared professed (see Ether 3:2).
It is the burden of scripture, particularly the Book of Mormon. Adam fell. His posterity fell with him, in the sense that all mankind-no one excepted-became, through conception (see Moses 6:55), subject to a fallen nature, a nature which must be put off through sincere repentance unto Christ.
Though we are not heir to an “original sin”-a taint that many Christians think entailed upon the posterity of Adam and Eve as a result of their disobedience-we are subject to the Fall and thereby in dire need of redemption.
In fact, the Fall and the Atonement are a package deal, a joint doctrine; there is no place in the Book of Mormon where the atonement of Christ is taught wherein the fall of Adam is not also taught or implied. If there had been no fall, there would have been no need for atonement. This is true on an individual as well as a cosmic basis.