Each of the six trustees selected to organize the Church as a religious body had been baptized before the Church was organized.
In Essentials in Church History, Elder Joseph Fielding Smith explained it was necessary for them to be baptized again because "baptism is the doorway into the Church as well as for the remission of sins. There had been a few others baptized before the sixth of April. Some of those previously baptized raised the question as to why they should again be baptized."In the 1947 Melchizedek Priesthood study guide, Elder Smith elaborated further, saying that the requirement for all who had been baptized before April 6, 1830, to be rebaptized is consistent with the teachings of the Lord.
"We have a like situation among the Nephites and Lamanites when Our Redeemer appeared to them," Elder Smith wrote. "Before that day they were subject to the law of Moses, although they had practiced baptism from the beginning for the remission of sins. (D&C 84:23-27.) And baptism was the entrance into the Church as it was established among them at that time, yet the Savior commanded Nephi, son of Nephi, to be baptized and to baptize the other disciples whom he had chosen and then the people, although Nephi and the disciples had previously been baptized. (3 Ne. 7:25-26; 19:10-14.)"