First and foremost the institution of the potlatch is there to send the message among the upper classes that material goods are secondary in importance to non-material station.
Honor is more important than wealth. A leader who impoverishes himself in the pursuit of a higher honor gains the esteem of his peers and dignifies the status of his subjects.
The national sabbatical year is the Scriptural analogue to the potlatch. Its message too is, first and foremost, that the non-material is more important than the material.
That the Children of Israel never really dared to risk a sabbatical year testifies to the weakness of their conviction in a political governance that is truly spiritual.