In verses 10 and 11, Jacob had emphasized that not following Jehovah’s commandments would result in destruction. In verses 14 and 15 the destruction is again predicted, but not upon those who oppose Jehovah. The current population will prosper if they keep the commandments, and in the future, their enemies will be finally defeated as the Messiah comes to destroy all those who do not believe in him.
Thus, Jacob presents two pictures. Both emphasize destruction, but the first is to his people if they do not repent. The second is upon their enemies, should his people repent and remain faithful. That is one of the things that is to come. The timing is unknown, but the promise is sure.
Nephi had seen a vision of the future that saw fire, tempests, and destructions associated with the coming of the Messiah. While the context of Nephi’s vision was the coming of the Savior to Bountiful, it is not likely that at this time, which was so much earlier than those events, that they would have been clearly separated. Indeed, we still expect destructions to precede Christ’s second coming.