Section 132 of the Doctrine and Covenants purports to be God’s explanation of why ancient prophets were allowed to have multiple wives and concubines. The revelation is in the form of an answer to Joseph’s question. Verse 1 sets the tone for the entire section by assuming that God approved heartily of the “doctrine” of polygamy:

Verily, thus saith the Lord unto you my servant Joseph, that inasmuch as you have inquired of my hand to know and understand wherein I, the Lord, justified my servants Abraham, Isaac, and Jacob, as also Moses, David, and Solomon, my servants, as touching the principle and doctrine of their having many wives and concubines (italics mine).

Thus, with no prefatory argument, Joseph Smith resolved for the LDS mind the question of whether or not God approved of the Old Testament practice of plurality of wives. Joseph bypassed the whole issue by saying that not only did God tolerate it, He actually required it.

This argument is suspended (securely, some Mormons think) from Joseph Smith’s version of the story of Abraham. According to Section 132 verse 35, God commanded that Old Testament prophet to take Hagar the handmaid of his wife as a concubine so that he could have the seed that God had promised him. But anyone who reads Genesis 16 can see the holes in this argument. God didn’t tell Abraham to take Hagar, Sarai did; and in verse 5 of Genesis 16 she admits that this, in hindsight, wasn’t a very good idea. (In fact, today’s bloody conflict in the Middle East shows the outcome of the rivalry between those who claim to be descended from Abraham’s two sons.)

For more information, see The Mormon Mirage 3rd Edition:  A Former Member Looks at the Mormon Church Today(Zondervan, 2009). Also available as an audiobook and as an expanded-text E-book for Nook, Kindle and other reading devices.