In his fourth chapter (the first chapter in part two,
entitled ‘Making a Payment On one’s Debt), 
Professor Anderson goes on to point that this notion of sin as a debt,
is clear enough even in the latter part of the OT, and he points in particular
to Is. 40.2.  He also points out that
when sin is viewed as debt, then the concept of satisfaction or payment of the
debt cannot be far behind.  Thus Isaiah
says ” Speak tenderly to Jerusalem
and declare to her that her term of service is over, the debt owed for her iniquity
has been satisfied. For she has received double for all her sins.’ in that
verse. 

The imgery here combines the
notion of slavery, and sin as a debt, so that we have sin as both a sort of
bondage from which one must be redeemed like a slave, and the notion of being
in debt, and so needing to do debt service. “When the debt slave has worked for
a sufficient amount of time, the debts will be considered repaid and the term
of slavery will end.” (p. 47).  Israel, in other words, was sent off into exile
in Babylon to
repay a debt…a sin debt.  God even says
in Is. 50.1— ‘to which of my creditors was it to whom I sold you off? You
were only sold off for your sins”.  

But
it is not just sin language that comes into the orbit of commercial
diction,  even the language about making
a vow to God is invaded by such vocabulary. The psalmist says “I pay my vows in
the presence of his worshippers” (Ps. 22.26). 
But this vow/payment is in response to a divine deliverance as the
earlier part of this psalm, recited by Jesus from the cross no less,
shows.   In the OT a sin offering, in fact
does not repay a debt, rather it cleanses the sanctuary from impurity.  The language of atonement is originally not
intermingled with the language of commerce. (see p. 53).  

But how did Israel pay for her sins while in
exile? Anderson
theorizes that Isaiah conceives of suffering as a means of paying down the sin
debt. It seems pretty clear from the Sifre of R. Nehemiah (3^rd century
A.D.) that by Mishnaic times this was how suffering was viewed, as a payment
for sins.  The question is whether one
already finds it in Isaiah or not.  Anderson has no doubt: “for the author of Second Isaiah, Israel’s sins at the close of the First Temple
period had put her over her head in debt. Decades of penal service in Babylon would be required
to satisfy its terms.”  (p. 54) 

One may well wonder where the grace and mercy
of God is in all this calculation.   God
comes across as a parsiminous accountant. Anderson
responds that God set up things so that sins have definite consequences, and so
it is word of grace, and a relief, when God says–you’ve paid for your crime,
now be set free. The punishment is not infinite but rather proportionate.   But this sort of mercy, falls far short of
the sort of grace and truth seen in the atoning death of Jesus, as we shall
have occasion to say later.