Not every statement made by a Church leader, past or present, necessarily constitutes doctrine. A single statement made by a single leader on a single occasion often represents a personal, though well-considered, opinion, but is not meant to be officially binding for the whole Church. With divine inspiration, the First Presidency...and the Quorum of the Twelve Apostles...counsel together to establish doctrine that is consistently proclaimed in official Church publications. This doctrine resides in the four “standard works” of scripture (the Holy Bible, the Book of Mormon, the Doctrine and Covenants and the Pearl of Great Price), official declarations and proclamations, and the Articles of Faith. Isolated statements are often taken out of context, leaving their original meaning distorted.

LDS Newsroom, "Approaching Mormon Doctrine," (4 May 2007)

http://www.mormonnewsroom.org/ldsnewsroom/eng/commentary/approaching-mormon-doctrine