We know but little of what occurred among the Nephites in Jacob's time. The people, however, appear in some respects to have fallen into sin. They had grown in worldly pride and devoted much time and energy to the search of wealth. By reason of their isolated position and because the Jews had abused the principle of plural marriage, the people of Lehi had been commanded that each man should have but one wife. Some of them did not heed this special law and took other wives, not only without God's sanction but entirely contrary to his express command. Indeed, they committed other grievous sins, excusing themselves therefor by quoting the actions of Kings David and Solomon, his son. At this the Lord was greatly displeased and he instructed Jacob to reprove them sharply. This, he did in the temple. He re-affirmed the law that the Nephites of that age should have only one wife, but he added, in the name of "the Lord of Hosts," that if he wanted to raise up a holy seed unto himself, he would command his people. This, we have reason to believe he did, though we find no direct statement on the matter.
Plural marriage is wrong where the Lord does not permit it. And the Lord, who commands his people to be loyal and law-abiding, is not going to give his consent to law-breaking. Matrimony, whether single or plural, is sanctified by the commandment of God, but he will not command his people to break the laws of the land. "Let no man break the laws of the land, for he that keepeth the laws of God hath no need to break the laws of the land." (D. and C. 58:21)