Jarom & Omni

Jarom 1:9

...But 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.

Omni 1:6

For the lord would not suffer after he had led them out of the land of Jerusalem and kept and preserved them from falling into the hands of their enemies, yea, he would not suffer that the words should not be verified, which he spake unto our fathers, saying that: Inasmuch as ye will not keep my commandments ye shall not prosper in the land.

This is one of the most often repeated messages in the Book of Mormon and it is a promise that is extended to all people. If we keep the commandments of God we will prosper, if we don't keep his commandments, we won't prosper. In Jarom the Lord had just delivered the Nephites from the hands of the Lamanites, in Omni the Lord had just caused the more wicked parts of the Nephites to be destroyed. So we can see both sides of the promise fulfilled one after the other. I don't doubt that the Lord would have the more wicked part of the Church destroyed if we fail to keep the commandments that we have been given as well.