Is The Atonement a Commercial Transaction?

David Allen, professor of theology, in writing against "limited atonement" said, in answer to a question:

"In a nutshell, you are assuming that the atonement is a commercial transaction rather than a penal transaction, as Scripture teaches. In a commercial transaction, if the debt is paid, it cannot be paid for again. If so, then an injustice is done."  (SEE HERE)

Allen repeats what those who believe in unlimited and indefinite atonement often say.  They say that those who believe in special (or limited) atonement make the error of seeing the atonement as "a commercial transaction."  He then says that the truth is that the atonement is a "penal transaction."

In response, I object to Allen implying that men like John Piper (who Allen is critiquing) reject the idea that the atonement was a "penal transaction."  He implies that one cannot believe that the atonement is BOTH a commercial and penal transaction. 

Further, the atonement being a penal transaction poses the same difficulty for Allen as does the atonement being a commercial transaction.  Further, there is in Scripture a mixing of these two concepts, so that they are not mutually exclusive as Allen imagines.  When a criminal is being punished for his crimes (penal), he is at the same time "paying his debt" to the state whose laws have been transgressed.  Jesus likened sin to debt when he told us to pray "forgive us our debts as we forgive our debtors." 

Just as it would be wrong to collect a debt twice (commercial transaction) so it would be wrong to punish two men for the same crime (penal transaction), or punish one whose legal debt has been satisfied.

Allen admits that the commercial view of the atonement poses problems for Allen and his universal atonement view, so he rejects it, though the Scriptures support it.  What Allen needs to realize is that even his "penal transaction" view gives him the same difficulty.  It is "double payment" versus "double jeopardy."