Verse 4 presents the closing "frame" of Nephi's narration of the journey eastward. He has presented the gross historical details, has extracted a moral, and now closes this episode with a reference again to the historical - in this case a number of years. While we are interested in the number of years from a purely historical point, the number of years is not necessarily as important to Nephi (he begins with "for the space of many years" - and then delineates them). The function here is more than to mark the passage of time, but to close a literary unit.