Mormon gave us the information about Nephi the elder’s departure in 3 Nephi 1:2. He repeats it here for emphasis. There is a passing of righteousness. It is confirmed in that this righteous man does not return. Symbolically, Mormon is emphasizing the departure of general righteousness from the land.
“Whither He Went No Man Knoweth”
Mormon has not emphasized it, but he has drawn some important parallels between Nephi the elder and Alma the Younger. Both had been sitting chief judges, and both left the political position to preach to the people. Both had tremendous spiritual experiences, and both have a disappearance rather than a death. In this verse we have Nephi departing the land, and no one knowing where he went. Compare this to the account of Alma the Younger:
Alma 45:18-19
18 And when Alma had done this he departed out of the land of Zarahemla, as if to go into the land of Melek. And it came to pass that he was never heard of more; as to his death or burial we know not of.
19 Behold, this we know, that he was a righteous man; and the saying went abroad in the church that he was taken up by the Spirit, or buried by the hand of the Lord, even as Moses. But behold, the scriptures saith the Lord took Moses unto himself; and we suppose that he has also received Alma in the spirit, unto himself; therefore, for this cause we know nothing concerning his death and burial.
The idea that Alma was taken up by the Spirit as was Moses is not included in the statement about Nephi, though it is implied.