In 2 Nephi 1:20, Lehi said, "[God] hath said that: Inasmuch as ye shall keep my commandments ye shall prosper in the land." Lehi repeats this stipulation over and over because he wants his sons to keep the commandments. After he is gone, he wants them to prosper, and Lehi knows that the way they will prosper is if they keep the commandments. These words of this promise are mentioned predominantly in the book of Deuteronomy. Lehi remained true to his prophetic calling to establish firmly the principles taught in Deuteronomy, the book of scripture that had been found during Lehi’s young adulthood. Many passages and practices embedded in Deuteronomy, along with Isaiah and the Psalms, will persist down through the centuries of Nephite righteousness, as well as among the teachings of Jesus.
Book of Mormon Central, "How Is Prosperity Defined in Nephi’s Small Plates? (Words of Mormon 1:6)," KnoWhy 383 (November 21, 2017).