President Joseph Fielding Smith (1876–1972) explained why Jesus commanded the Nephites to be baptized again:
“When Christ appeared to the Nephites on this continent, he commanded them to be baptized, although they had been baptized previously for the remission of their sins. … The Savior commanded Nephi and the people to be baptized again, because he had organized anew the Church under the gospel [see 3 Nephi 19:7–15; 26:17]. Before that it had been organized under the law [see 3 Nephi 9:15–22; 11:10–40; 12:18–19; 15:4–10].
“… For the same reason Joseph Smith and those who had been baptized prior to April 6, 1830, were again baptized on the day of the organization of the Church” (Doctrines of Salvation, comp. Bruce R. McConkie, 3 vols. [1954–56], 2:336).