4 And I command you that ye shall write these sayings after I am gone, that if it so be that my people at Jerusalem, they who have seen me and been with me in my ministry, do not ask the Father in my name, that they may receive a knowledge of you by the Holy Ghost, and also of the other tribes whom they know not of, that these sayings which ye shall write shall be kept and shall be manifested unto the Gentiles, that through the fulness of the Gentiles, the remnant of their seed, who shall be scattered forth upon the face of the earth because of their unbelief, may be brought in, or may be brought to a knowledge of me, their Redeemer.
This verse is quite sobering. Jesus is saying that the people in Jerusalem could have had knowledge of the Nephites and the Lamanites as well as other scattered disciples of Christ, but they chose not to learn about them because they were unwilling to ask. They could not look beyond their vision of Israel and inquire more deeply into the words of the Lord.

What knowledge and insight are we missing because we are not willing to ask?

We don’t have the full story here due to the limited amount of early Christian records. It is very possible that the Apostles did ask and knew more than we can see in our scriptures today. If John the Revelatory saw the restoration and spoke of the Angel Moroni as we believe, then it is possible that he and others knew of the Nephites
I am also comforted by the fact that the Lord will always provide a way for vital knowledge to come forth in due time – even if that knowledge has to come from out of the dust. He will not leave us guideless or comfortless.