In his speech, Jacob stresses the benefits of waiting for and believing in the Lord. He promises destruction during the Savior's second coming to those who did not believe and protection to those who did. While not exclusive to Mormonism in any way, this concept is played upon heavily in the church.
The similarities between the Nephites awaiting Jesus's first coming and modern-day Mormons awaiting Jesus's second coming are emphasized--the movie The Testaments stands as a good example. The Nephite society is depicted as having believed in the Messiah for so long that most people have lost faith. Similarly, Mormons have been in it's-almost-the-end-of-times mode for a very long time. The church wants us to hold out and continue assuming that the day of our vindication is just around the corner.
Not only does this strategy keep people scared and obedient, but it gives them hope that a lifetime of being peculiar and removed from the mainstream will be rewarded when Jesus returns. This will be accompanied by all those self-righteous evangelicals who hated Mormonism suddenly realizing that they've been wrong the whole time...right before they're destroyed for their wickedness.
Jacob subtly pitches a similar idea to his people (and, therefore, Joseph Smith subtly pitched the idea to his followers)--hold out, remain obedient, and one day everybody will know you were right, God will destroy them, and you will be rewarded.
But it's just a way to keep the people in line.