These two verses are critical for understanding the rest of the Book of Mormon. Jacob begins with two names that will form the essential cultural dichotomy in the Book of Mormon, Lamanites and Nephites. The statement begins by noting that those who are not Lamanites are Nephites. It is a binary division.
Jacob explains that these two collective terms include tribal names. There are Jacobites, Josephites, Zoramites, Lemuelites, and so forth, but Lamanite and Nephite are not used in the sense of tribal designations. Specifically, Jacob says “I shall call them Lamanites that seek to destroy the people of Nephi, and those who are friendly to Nephi I shall call Nephites.”
This begins the essential division between “us” and “them” which characterizes so many ancient societies. The division is not tribal and is in no way genetic. It is a political designation, which explains how it is so easy for Book of Mormon peoples to cross the boundaries. Lamanites easily become Nephites by believing as Nephites do, and when Nephites no longer believe as Nephites are supposed to, they become Lamanites. As Jacob say, the difference is whether anyone is friendly or an enemy.
It is also important to remember that it was Nephi who discussed the cursing of the Lamanites and their skin of blackness. For Jacob, that doesn’t enter into his discussion of the difference between Lamanite and Nephite at all—except that the skin of blackness defines the character of the enemy. Most importantly, Jacob never says that skin pigment was a difference. It is only whether one is a friend or an enemy.