As Jacob transitions from discussing the sin of thinking oneself better than another, he returns to the idea that not all people are under condemnation. He had said that the Nephites were, as yet, living the commandments. Then launched into the sin of those who were not.
Similarly, the transition recognizes that not all are under condemnation. There are those who are pure in heart. They have been faithful, and are admonished to continue to be faithful. Those people are not the target of his sermon. The next phase of the sermon begins by pronouncing a wo upon those who are not pure in heart.
The way that Jacob will begin to make this case is interesting. He brings the Lamanites into the issue. The Lamanites are the enemy, and most people create divisions between the in-group and the out-group. The in-group is good, and the out-group is not as good. In the ancient world, it was often more dramatic, and for the Nephites, it was an even greater division. Nephites were good. Lamanites were the opposite. The social division had been reinforced by prohibitions of intermarriage. They were complete, and dangerous; they were opposites.
In spite of that difference, Jacob uses them as a comparison against which the Nephites do not fare well. In absolute contrast to cultural expectation, Jacob declares that the Lamanites “are not filthy like unto you.” Built into that reversal is the reminder that the negative aspect of the promise of the land is that the Nephites would be destroyed if they do not live the commandments. Jacob does not threaten them with destruction, but with scourging. Perhaps there are sufficient numbers of righteous to forestall destruction, but not to prevent serious problems.