Jacob 3 continues the sermon from Jacob 2. In it, Jacob points out that the only reason a rival tribal group is hostile to the tribal group to which his audience belongs is because of the sins and errors of their fathers. Having just torn into the sins of the fathers of his own tribal group, Jacob concludes that there is no reason to consider the other tribe to be more wicked.
He seals that with a commandment from God: “Wherefore, a commandment I give unto you, which is the word of God, that ye revile no more against them because of the darkness of their skins; neither shall ye revile against them because of their filthiness; but ye shall remember your own filthiness, and remember that their filthiness came because of their fathers.” In other words, stop hating the “others” based upon a perception of them which is man-made.
In the narrative, the two tribal groups are all descendants of the same family group, and they are only 2-3 generations away from those family founders. Both have expressed hatred for each other and Jacob’s group is already referring to the other one as dark, loathsome, and cursed. That’s all a perception, though: in only 2-3 generations, we don’t see any sort of situation that leads to a sudden change in human skin pigmentation. The racism/tribalism in this case is all in the heads of the people suffering from that disease, as it always is.
With a comment along the lines of Jesus’ about clearing the obstructions from one’s own eyes before helping another to clear a minor irritant, Jacob instructs these wayward fathers to remember their own children. The implication being that they are not immune from committing the same paternal errors associated with the “others.” They are, in fact, cited as being more sinful because of their neglect of their families, and that they are putting their nation on a path to destruction. All this, of course, is connected back to their seeking of wealth and social divisions based upon wealth.
In sum, Jacob emphasizes the equality of man before God and the need to treat each other with equality and dignity: anything less than that puts us on the path to destruction as a nation.