1 Nephi 19:3

And after that I had made these plates by way of commandment, I, Nephi, received a commandment, that the ministry, and the prophecies, the more plain and precious parts of them, should be written upon these plates; and that the things which were written, should be kept for the instruction of my people, which should possess the land, and also for other wise purposes, which purposes, are known unto the Lord;

After I made these plates because the Lord commanded it, I received another commandment. The Lord told me to write the ministry and prophecies on these plates. He wanted the most important and precious parts written here. These writings would teach my people who would live in this land. The Lord had other wise reasons for this too.

After I made this new set of plates as commanded, I received another instruction: write the spiritual teachings and prophecies here—the clearest and most precious parts. These writings would teach my descendants who would one day inherit this land. The Lord has other purposes for them too, which only he knows.