Mormon has used the same historical events in two different places, for two very different reasons. In 3 Nephi his intent is to show that the three Nephites were worthy and righteous men. Therefore he presents their miraculous preservations, and concludes with the statement that many were converted.
In the current text, where the events are placed in more chronological context, the emphasis is not on the miraculous preservation as much as on the persecution. The conclusion is therefore not hopeful because of the conversions, but foreshadowing the downfall of the Nephite nation because of the wickedness that would allow the people to persecute such righteous men.
We have in these two instances a wonderful example of the way that Mormon perceived his text and task. Mormon has taken exactly the same events, and virtually the same language, and placed them in two completely different contexts to prove two very different points. In doing this, Mormon is flexible with his use of time in the text. In the first instance, the good effect of their preaching is to emphasize the positive aspects of their ministry. In the second set, the persecutions themselves are indications of great apostasy. While it is quite likely that there were very faithful people at the very same time as the faithless were persecuting them, Mormon’s use of the events serves to segregate those pictures into a more discrete image than would have been present in a modern historical rendition of events.
Mormon has a spiritual purpose in his writing, and we must always remember that his spiritual purposes take precedence over strict and dispassionate historical recording; if ever he records anything like a dispassionate historical recording.