In this verse, Thompson sees the fulfillment of the structural category of the witness statement (Thompson p. 125). The suggestion is that Jacob becomes the representative witness. Jacob, however, is much more that a witness, he becomes an accuser against the witness of God.
Sociological Information: Jacob shakes off his garments. Regardless of the nature of the cultural heritage of Israel, regardless of the hetero- or homogeneous nature of Jacob's audience, the action of shaking the garment would have a clear symbolic connection for those listening to Jacob. Both visually and oratorically, Jacob has contrasted himself with his audience.
The very fact of the very public ritualized purification demonstrates Jacob's highly visible and important position in the community. For example, should child perform exactly the same ritual, and say exactly the same words, few would take either the actions or the words to heart. In the person of an important and visible member of the community, done in major public discourse, sanctioned by the political ruler, the context of place and person makes this ritual particularly impressive. The impression it had to leave confirms the social acceptance of Jacob's right to even make such a gesture.
We have been given to understand that Jacob was a religious teacher of the people, this event gives us more accurate picture of his status. Jacob must have been the religious leader, being probably the only person besides Nephi who could have even made this statement.
The sociological picture then becomes a little more clear in representing a society of sufficient population to allow for a political/religious division. The addition of other people to Nephi's original group that fled from his brothers would have to have been augmented significantly to create a minimum of two such powerful people in the community.