Mormon 5:15

and also that the seed of this people may more fully believe his gospel, which shall go forth unto them from the Gentiles: for this people shall be scattered, and shall become a dark, a filthy, and a loathsome people, beyond the description of that which ever hath been amongst us; yea, even that which hath been among the Lamanites; and this because of their unbelief and idolatry:

Also, the children of this people will believe his good news more. The good news will come to them from the Gentiles. This people will be scattered. They will become dark, dirty, and hated. They will be worse than anything we have ever seen. They will be worse than the Lamanites. This will happen because they don’t believe and worship idols.

And this record will help the descendants of my people believe the gospel more fully, when it comes to them through the Gentiles. Because this people will be scattered. They’ll become dark, degraded, despised—worse than anything we’ve ever seen, even worse than the Lamanites. All because of their unbelief and idolatry.