Why does Nephi specifically affirm that they kept the law of Moses "in all things"? What would be involved in doing this? From his sacrifice and deliverance in obtaining the plates of brass, Nephi knew the seriousness of obeying the law as completely as possible. Nephi’s determination in this regard set a strong precedent that ran through Nephite societies and governments in the lands of Nephi with King Noah, in Zarahemla under King Benjamin, and on down until the coming of Christ among the Nephites in Bountiful and his pronouncements regarding His giving and fulfilling of that law (3 Nephi 15). Nephi testifies that his people "did prosper exceedingly" in the land, as their crops and herds flourished (5:11), as the law in Deuteronomy particularly assured. How does it help promote righteousness and spirituality to strive to observe the requirements of the Lord with exactness?
John W. Welch, The Legal Cases in the Book of Mormon (Provo: Brigham Young University Press, 2008), 12–16, 33–47.