Robinson and Mensana have changed their points of view. Robinson goes even so far as to offer Mensana a sack of grain.
But the shipwrecked Mensana says: "I shall not add anything and I shall not substract anything." Or in the words of Gesell: "I must decline your offer, for it would mean interest - not indeed positive, but negative interest. The receiver, not the giver of the loan, would be a capitalist, and my religion does not permit usury; even negative interest is forbidden..." (Gesell, A Story of Robinson Crusoe) 
He had learned this principle once and therefore he sees the balance in performing work.