Just as we saw with the oath of Zoram (1 Nephi 4:37) a simple declaration has altered the entire nature of the proceedings. Where they began in chains, they end in celebration. Where the physical presence of the intruders was considered dangerous, a simple declaration makes them kinsmen, and welcome guests. This rapid shift of position is precisely the kind of social relationship that kinship would create. The declaration of genealogy is for this very purpose, to sort friend from foe.
Limhi declares a day of rejoicing not simply because Ammon has arrived, but because he now “know[s] of a surety that my brethren who were in the land of Zarahemla are yet alive.” The question we should ask is why he would ever doubt it. Zeniff had left with many fewer people that were left in Zarahemla. Why would Limhi have even imagined that “his brethren” in Zarahemla would not be alive?
When Zeniff leaves with his party, the union of the Nephites and Zarahemlaites was reasonably new, and certainly would have already seen its difficulties. It is probably that some of the contentions that reached a head in Benjamin’s reign had already begun to surface with Limhi left. When combined with the years out of contact, the contentions may have been imagined to have increased to the point where the lineal/cultural Zarahemlaites might have turned on the lineal/cultural Nephites, who were Limhi’s “brethren.” In their difficult economic situation, Limhi’s people would have been unable to send a party to find Zarahemla, and the lack of communication from Zarahemla to them must have seemed fatalistic.