Redaction: It must be remembered that this verse artificially begins a new chapter. In the 1830 edition it would have followed the preceding verse with no break. This is continuation of the same sermon, and the analysis depends upon linking them back together.
Anthropological: Jacob now explicitly readdress his audience. This is a mixed audience, with both those who have been the subject of his admonitions and those who have been the victims of the prideful, rich, men. Jacob has been admonishing a set of men (the passage on polygyny precluding women from his condemnations) who apparently have two crimes, the second worse than the first.
The first crime was pride (demonstrated through the wearing of costly apparel) that caused the to believe themselves superior to their fellow villagers. The second involved polygyny, with women being taken away captive. Now that Jacob has made a shift in the audience he is addresses, he calls this part of the audience the "pure in heart."
There are three types of people Jacob may be including in the "pure of heart." the first would be the women and the children, whom he has just described as being of broken hearts (Jacob 2:35, the immediately preceding verse). The second type might be those who are being derided for not being as good as the wealthy (Jacob 2: 13). The third would be any who are righteous but not included in the two persecuted groups. While any or all of these three might be meant understanding this group most strictly is important because Jacob tells us that they are in danger of "destruction."
The first piece of information in discerning those whom Jacob is addressing as "pure in heart" is that they are threatened with destruction. The fact that this entire audience has assembled to hear Jacob at the temple, and that they have come expecting to hear the "pleasing word of God" (Jacob 2:8) and that they have until now been obedient (Jacob 2:4) rather eliminates the righteous men option. For all that they are falling into error (and Jacob specifically notes that they are beginning to be proud - Jacob 2:5), they are still sufficiently righteous to want to listen to "the pleasing word of God."
The second piece of information about those who would seek to destroy the pure in heart is that the only solution Jacob can offer is prayer! Of course it is always a worthy suggestion that one might pray, but is there no other recourse against imminent destruction? Where is law?
One again we must turn to reasonable speculation based on the anthropological hints provided in Nephi and Jacob's text. The most important datum to remember is that Nephi was selected King, and orchestrated a peaceful selection of the next King. Even though kingship would be embued with the divine, it appears to have functioned secularly as well. Thus we may be certain that there was a type of government available, and that there were both laws and means of enforcing those laws.
When Jacob is describing a destruction, he does not appear to be speaking rhetorically (though he will use the theme of destruction rhetorically in verse 3). Rather, this is a threat of sufficient weight that he begs those threatened to invoke the protection of God. What Jacob does not do is tell anyone that something illegal has occurred, or that the sanction of the local government has been called into play. To put it bluntly, if the "pure in heart" are being threatened with destruction, where are the police?
In any internal strife we would expect that the established modes of legal sanction would be called into play. Therefore, if those threatened with destruction were the poor who were thought to be lesser than the rich, then we would expect the rich to be told that the poor would be protected. The very fact that social division in a relatively small village is so destructive that it becomes the reason for Jacob's condemnation of the pride of the rich tells us that Jacob would use all available power to prevent such discord let alone any threat of physical violence - of destruction.
The only place where we have a conflict that can lead to destruction where Jacob cannot use the authority of government is outside of he bounds of the village. There is no regional government this point in time with each village and city being fairly autonomous, although smaller hamlets might choose to affiliate with a nearby village. In this social structure, the village of Nephi has no legal authority over other villages.
We can then set the scenario that Jacob is describing. The reason the "pure in heart" must pray for deliverance is that there is no legal recourse for them. Perhaps war might have been an option, but if the women who are sent to be wives in these foreign villages are going due to negotiations entered into a part of the trading exercise, then there would also be little legal or moral support for war, since those who were receiving the women would be doing so in good faith, and according to their culture.
This scenario highlights the women as the "pure in heart" who are in danger, and explains why the only recourse is prayer, but it does not adequately explain the "destruction." While a real threat, Jacob is probably exaggerating the physical danger. It is very unlikely that anyone incurring a second wife would do so specifically to endanger her. In the context of trade, either the relationships to the trading partner or the very expense of receiving the bride mitigate against destroying her. Thus the "destruction" appears to refer to the removal of the women from their village, and probably from their religion (there is no indication of any other village of Nephite religion). It is a social destruction, not a physical one.