I recommend Bruce Marshall’s review essay of Gary Anderson’s Sin: A History especially for these last two days of Christmas. Marshall shows the interesting history of how sin came to be understood as debt—rather than simply a burden or a wound—and then offers an excellent defense of this understanding of sin. For debt implies that repayment must be made. God could have simply forgiven our sins, washed them away, but by making us debtors he allows humans to be part of their own salvation. One of our own, God become man, made the payment for our sins and then allows us to join our own small efforts to repay our debts to his. It gives new meaning to the hymn we all were so recently singing: “O to grace how great a debtor, daily I’m constrained to be!”
