Answer
Doctrine and Covenants is one of the “standard works” of Mormonism, also known as the Church of Jesus Christ of Latter-day Saints (LDS). Along with the Book of Mormon, Pearl of Great Price, and the Bible, Doctrine and Covenants is a text the LDS considers authoritative in matters of doctrine. Of course, the Mormon faith qualifies use of the Bible with the words “so far as it is accurately translated,” which in practice means “so far as it agrees with Mormon writings.”
Originally, Doctrine and Covenants contained two main sections. The first was an extensive collection of lessons about Mormon doctrinal beliefs. The second section featured supposed “revelations” given to prophets of the LDS. Since the early twentieth century, most copies of the text have excluded the first, doctrinal section. Passages from the second portion, containing revelations from supposed prophets, are viewed as having mixed authority within the LDS. The content of Doctrine and Covenants has been revised numerous times, both to add new revelations and to correct or remove older ones. Some sects of Mormonism are divided over which edition of these texts is correct.
Of particular note are two “declarations” included in Doctrine and Covenants. These do not contain actual revelations themselves, but rather statements indicating that the LDS had received a particular revelation. The first, added in 1890, reversed Mormonism’s previous endorsement of polygamy. The second, given in 1978, removed the Mormon restrictions on non-whites being members of the priesthood. Needless to say, these were large-scale changes in LDS doctrine.
As with other Mormon scriptures, the contents of Doctrine and Covenants often contradict the Bible. That doesn’t bother the Mormon because, in practice, the LDS considers the Bible secondary to its own, later writings. Among the false doctrines included in Doctrine and Covenants are the teachings that God has a flesh-and-blood body, that human beings can become gods just like God, and so forth. The combination of open changes in doctrine and non-biblical views makes Doctrine and Covenants an invalid source of spiritual truth.