“the word of the Lord was verified, which he spake unto our fathers, saying that: Inasmuch as ye will keep my commandments ye shall prosper in the land.
And it came to pass that the prophets of the Lord did threaten the people of Nephi, according to the word of God, that if they did not keep the commandments, but should fall into transgression, they should be destroyed from off the face of the land.” (Jarom 1:9-10)
This promise stated several times in scripture. I know that it is true, because I can attribute my prosperity, as well as my poverty, to my willingness to keep the commandments.
This is what I wrote previously after reading Jarom 1: Living As If Jesus Is With Us