The Practice of Polygamy
Authors: Brian C. Hales and Laura H. Hales
In Old Testament times, patriarchs like Abraham and Jacob practiced polygamy, which seems to have been divinely approved. In the early nineteenth century, there were some fringe religious groups who toyed with the practice, but in general it was repugnant to most pre-Victorians. Monogamy was rightly viewed as the marital standard. But in 1840s Nauvoo, Joseph Smith taught that God commanded that polygamy be practiced among the Latter-day Saints.
Though described as part of the restoration process, it is not a needed salvific ordinace but a practice that is sometimes allowed as part of a much grander doctrine revealed by the Prophet. Celestial marriage allows God's children to be eternally married and to become like our exalted Heavenly Parents. This exaltation is offered to all righteous couples sealed in the new and everlasting covenant of marriage and is not conditional on a plurality of wives.
Learn more about this topic in A Reason for Faith: Navigating LDS Doctrine and Church History