In the Book of Mormon, there are multiple accounts of Alma the Younger’s visitation of an angel:
If Joseph Smith had dictated the Book of Mormon on the fly we would reasonably expect him to either be inconsistent in the different versions of the event, or to use the same memorized language each time. If this was a true account of Alma the Younger then we would reasonably expect the main details to be the same but with slightly different language each time as the event was described to different people at different times.
We see the latter, for example there is greater emphasis on the sons of Mosiah in the account which Mosiah recounts and we also see slightly different wording used to describe the earth shaking:
Doesn’t this sound like someone describing an actual event? John Welch summarizes this point:
Despite the fact that Mosiah 27 is separated from the accounts in Alma 36 and 38 by the many words, events, sermons, conflicts and distractions reported in the intervening one hundred pages of printed text, these three accounts still profoundly bear the unmistakable imprints of a single distinctive person, who throughout his adult lifetime had lived with, thought about, matured through, and insightfully taught by means of his powerful and beautiful conversion story.– John Welch, “Three Accounts of Alma’s Conversion,”153
How did Joseph Smith manage to not only produce an internally consistent book but also put himself in the position of the characters?