What is your understanding of The Law of Sarah?
First of all an explanation as to what it is:
“Concubines were common during this time, and I find it remarkable that neither Sarai nor Abram had resorted to such means of having children before they did. It was ten years after they left Haran before Abram took Hagar to wife-ten years since he had first received the promise. There is no indication that he ever reproached Sarai for her barrenness, though as the years passed, the flocks and herds increased, but Abram didn’t.
“Because in the scriptures years of history are condensed into a few words, it sometimes seems that biblical characters lived charmed lives. This brevity can lead to the misconception that favored servants of God were spared day-to-day frustrations, that they were immune to crushed hopes and human emotions. Nothing could be further from the truth. Yet only once did Abram betray his grief. In secret, he chided the Lord, saying that he from whom a great nation was to spring had only a servant for an heir. The Lord responded with a reiteration of his promise.
“Acting under the ‘law of Sarah’ (see D&C 132:65), Sarai suggested that Abram accept Hagar as his concubine. They hoped that in his doing so, the promise might be fulfilled. Hagar was an Egyptian, given to Sarai by Pharaoh and taken by Abram and Sarai out of Egypt to a foreign land and a strange way of life. Likely she was young, a favorite of her mistress, and likely she had no say in the matter. She was considered property and was so subservient that the thought of her consorting with Abram gave Sarai the least possible pang. Her child, if she had one, was to be raised by Sarai as her own. The arrangement was an expedient, physical adjustment, with Hagar providing a fertile womb, nothing more.” (Jerrie W. Hurd, Our Sisters in the Bible [salt Lake City: Deseret Book Co., 1983], 9 – 10)
“‘Sarah gave Hagar to Abraham in accordance with law. It is known that, according to the Code of Hammurabi, which, in many respects, resembles the later Mosaic law, if a man’s wife was childless, he was allowed to take a concubine and bring her into his house, though he was not to place her upon an equal footing with his first wife. This was the law in the country from which Abraham came. A concubine was a wife of inferior social rank.’ (SS, 831.)
“The ‘law of Sarah’ seems to be the approval given by the first wife for the husband to take additional wives, in order to ‘raise up seed’ unto the Lord (D&C 132:61, 64-65). Even though God commanded Abraham to take Hagar to wife, Sarah, as the first wife, gave her approval (D&C 132:34). It appears that if the first wife will not give her approval, however, after having been properly taught the priesthood propriety of such action, she is under condemnation and the husband is exempt from this ‘law of permission.’
“A caution should be issued in relation to this law. Currently this law and all principles pertaining to the practice of plural marriage have been officially suspended by The Church of Jesus Christ of Latter-day Saints. Since 1890, this has been the position proclaimed by the prophets of God.” (Hoyt W. Brewster, Jr., Doctrine and Covenants Encyclopedia [salt Lake City: Bookcraft, 1988], 317)
I also refer you to the Church’s Gospel Topics essay regarding plural marriage in Kirtland and Nauvoo, (Plural Marriage in Kirtland and Nauvoo)
The revelation on marriage required that a wife give her consent before her husband could enter into plural marriage. Nevertheless, toward the end of the revelation, the Lord said that if the first wife “receive not this law”—the command to practice plural marriage—the husband would be “exempt from the law of Sarah,” presumably the requirement that the husband gain the consent of the first wife before marrying additional women.
I would also add that my personal interpretation of D&C 132 is that the exception to the “Law of Sarah” spelled out in Verse 65 is limited in verse 64 as applying only to the man who holds “the keys of this [i.e., the sealing] power.” In other words: the President of the Church, as the one who held the keys to the sealing power (and as a necessary example for the rest of the Church), could theoretically enter into a plural marriage over the objection of his first wife; but no other man in the Church could have held such a prerogative.
In “Joseph Smith’s Polygamy: Toward a Better Understanding” (Greg Kofford Books 2015), at page 14 authors Brian and Laura Hales cite the above quotation from the Gospel Topics essay and add:
Understandably, the apparent injustice regarding the law of Sarah may seem unfair to some observers. However, if Brigham Young is correct that there is “no law in heaven or on earth that would compel a woman to stay with a man either in time or eternity” against her will, then the only women to practice eternal plurality will be those who choose to do so.