"And in as much as ye shall keep my commandments, ye shall prosper,and shall be led to a land of promise; yea, even a land which I have prepared for you; yea, a land which is choice above all other lands."
Nephi is promised that so long as he and his family keep the commandments of the Lord they shall prosper. They would also be led to the pomised land, which we know to be the Americas. This is a huge promise. And the Lord one He makes a promise will keep it so long as the other party does what they are expected and need to do. So, if the person making the covenant, meaning a promise between us and God, keeps the side they are supposed to then the Lord will give what was promised.
The promised land was kept a place apart from others by the power of God. It is a land preserved because it is a "Choice land above all others." The Lord saved it for a specific purpose.
Nephi promise from God receive. If family obey God they blessed will. Them lead promised land will. Happen God promise make give will if other person themself obey will.
Promise land preserve, save. God purpose have, above other land.