Prophets are not taught differently than the rest of us. They learn ’precept upon precept; line upon line…here a little, and there a little’ (Isa 28:10). The difference is a matter of speed, for the time interval between each precept is much shorter. Prophets are more adept at drinking living water from a fire hydrant because they have faster spiritual digestive systems. Nevertheless, the process is the same.
Accordingly, the prophet Mormon learned spiritual truths like everyone else—through the spirit of prophecy and revelation—after fervent prayer. Hereby, he learned the nature of translated beings. His prophetic progress is much like that of Alma who at first did not know the state of the soul between death and resurrection. His diligent inquiry gave us one of the greatest commentaries available on the spirit world (see Alma 40:3-26).
Jeffrey R. Holland
"As noted above, these three Nephites, as part of their translation experience, were also transfigured, caught up into heaven, where they ’saw and heard unspeakable things. And it was forbidden them that they should utter; neither was it given unto them power that they could utter the things which they saw and heard.’ (vs. 13-14)
"This circumstance and promise was so new to Mormon, who was reading and writing it nearly 400 years after it happened, that he did not initially know whether the three ‘were in the body or out of the body’ during such a heavenly experience, or whether they had moved permanently beyond mortality into immortality.
"So moved was Mormon by this promise and the account of their deeds that he inquired of the Lord about their state. In reply, the Lord informed him that translated beings were still mortal but that a special change, more permanent than transfiguration, was ’wrought upon their bodies, that they might not suffer pain nor sorrow save it were for the sins of the world…insomuch that Satan could have no power over them, that he could not tempt them; and they were sanctified in the flesh, that they were holy, and that the powers of the earth could not hold them.’ (vs. 37-39)
“This terrestrial condition, however, was not to be their final state, for when Christ came they would move from mortality to immortality in an instantaneous, deathlike transition.” (Christ And The New Covenant, p. 306 – 307)