Ever planned a big family event? It is crazy important to assign everyone the right spot. Not only at the tables but also in written invitations, announcements and such.
Now when the Jewish people where in exile in Babylon they had pretty much the same dilemma: Who belongs and what is their rightful place among us? They went to their priests and the priestly source created this wonderful list of the sons of Jacob.
This has nothing to do with a starving people seeking food south of the border. It is about assigning the right spot to the right people right here right now.