Between income and principal

A Ponzi scheme books principal as income. That is the essence of unsustainability. 

Ki tavouh el haaretz is a pun on exactly that matter. When you come to the land you will begin to harvest and book income as opposed to living off the principal. 

For the people of Israel the meaning of their purchase on their homeland is that it clearly delineates between income and principal. The true principal is the fount of deservedness. A society that is expert in defining what is principal versus what is harvest is a society that is clear about what is sacred, which is to say what is the source of productivity and fertility, i.e., where are lodged the blessings of children and land (Abraham's blessing) as well as the blessings of superiority to one's siblings, rivals or adversaries (Yitzchoq's blessing), what cannot be sold nor even really be alienated from one's person. 

To lose the presence of God is to forget what is sacred, it is to blur the line between principal and harvest, and it is to build society into a gigantic, unsustainable Ponzi scheme.