Socio-political: Either this verse is simple hyperbole to state that there were lots of people, or something more is going on. In this case, we must remember that these are Mormon’s words, and he is writing based on the text in front of him. Note the phrasing. There are lots of people “even so many that they did not number them.” The people are not numbered because there are many, but specifically because there are so many. This appears to indicate that some type of counting did occur from time to time, and that this time the number was so great that the count was not taken.
Just as a census was recorded in the Gospel of Luke (Luke 2:1-5) so we may have a record of a periodic census here. Similarly, the Roman census was for the purpose of taxation (Luke 2:5) and it is probably that the Zarahemlaite census may have had the same purpose. Mesoamerica had a very long tradition of dependent towns paying tribute to a city center. While Zarahemla was not as large nor as prosperous as Nephi, it apparently had increased significantly in influence during Benjamin’s reign, and this congregation of the population exceeded the normal counts of those who would attend the ceremonies in the central town.
Other possibilities would follow Old Testament censuses (Ex. 30:12; Num. 1:1-4, 26; 2 Sam. 24; 1 Chron. 21). “Generally the purpose was to prepare for war, but censuses were also taken as preparation to serve God (Num. 4:1-3, 21-23). In 1 Chron. 23, some kind of census appears to have been associated with David making his son Solomon the king, a situation somewhat analogous to Benjamin’s coronation of Mosiah. (Coutts, Alison V.P., et al. ”Complete Text of Benjamin’s Speech with Notes and Comments." In: King Benjamin’s Speech. FARMS, 1998 p. 506).
The next interesting thing about this count is that it appears that this gathering is exceptional. There would have been public gatherings all along, but this one was special, and drew larger than expected crowds. Why?
We can understand that the coronation of a new king is an exceptional occurrence, and that alone might suffice to explain the large crowds. However, we must also remember the brief glimpses we have had into the circumstances of Benjamin’s reign. It has not always been as peaceful as it is now, and Benjamin has forged a new society out of the conflicts generated from the combination of Nephite and Zarahemlaite under his father, Mosiah I. In addition, Benjamin has indicated a ceremony of naming. He will be giving the people a new identity. With the addition of the fascinating possibility of the archaeological situation, we may have Benjamin proclaiming this unification not only at a temple, but at the specific temple on which the people have begun to work (and on which their collective labor will continue to be required).
If we couple these circumstances with the probability of a Jubilee Year/New Century, this occasion is fraught with multiple meanings for the assembled crowds, and the very nature of their existence and identity will be effected by the ceremonies they are attending.