Who owes what to whom

What is the difference between moral obligation and debt?

Moral obligation is:

Debt is:

The author of Debt: The First 5,000 Years points out the profound moral confusion and the resultant justifying of violence:

"Majority of human beings hold simultaneously that (1) paying back money one has borrowed is a matter of morality, and (2) anyone in the habit of lending money is evil." 

"Money’s capacity to turn morality into a matter of impersonal arithmetic....", (and justify violence against one who fails to pay up.)