After the Savior told the Nephites that they were the “other sheep” mentioned in John 10:16 (see #30 WHO ARE THE “OTHER SHEEP” THAT CHRIST MENTIONS? LATTER-DAY SAINTS HAVE THE ANSWER), he told them:

I say unto you that I have other sheep, which are not of this land, neither of the land of Jerusalem, neither in any parts of that land round about whither I have been to minister. For they of whom I speak are they who have not as yet heard my voice; neither have I at any time manifested myself unto them. But I have received a commandment of the Father that I shall go unto them, and that they shall hear my voice, and shall be numbered among my sheep, that there may be one fold and one shepherd; therefore I go to show myself unto them (3 Nephi 16:1–3).

This continues themes that are prominent in the Book of Mormon: God’s care for all His children and the gathering of Israel.

On top of saying that Christ would personally visit to these nations, Christ tells Nephi that he would provide these nations with books out of which they would be judged. 2 Nephi 29:11–14 reads:

For I command all men, both in the east and in the west, and in the north, and in the south, and in the islands of the sea, that they shall write the words which I speak unto them; for out of the books which shall be written I will judge the world, every man according to their works, according to that which is written. For behold, I shall speak unto the Jews and they shall write it; and I shall also speak unto the Nephites and they shall write it; and I shall also speak unto the other tribes of the house of Israel, which I have led away, and they shall write it; and I shall also speak unto all nations of the earth and they shall write it. And it shall come to pass that the Jews shall have the words of the Nephites, and the Nephites shall have the words of the Jews; and the Nephites and the Jews shall have the words of the lost tribes of Israel; and the lost tribes of Israel shall have the words of the Nephites and the Jews. And it shall come to pass that my people, which are of the house of Israel, shall be gathered home unto the lands of their possessions; and my word also shall be gathered in one. And I will show unto them that fight against my word and against my people, who are of the house of Israel, that I am God, and that I covenanted with Abraham that I would remember his seed forever.

This confirms a notion found in later Latter-day Saint scripture that “religion is instituted of God” (Doctrine & Covenants 134:4). God is speaking to and ministering unto all nations, according to their language and understanding (2 Nephi 31:3), so that they can eventually be numbered with the covenant people of God.