The Debt Narrative in Piers Plowman.
The movement in PPl from the Old Law to the New, from the Dowel and Dobet to Dobest sections, is paralleled by a shift in the representation of debt from a metaphor of bondage (the debt of sin which only Christ can repay) to the freedom of the Christian (the debt of love, which only man can perform). This development also parallels the historical development of debt law and theory, from the old laws of contract and vicarious promise called to account, to that of a sealed bond by a debtor assuming personal responsibility. Abraham illustrates the vicarious responsibility Christ holds as borw to save helpless debtors in B.15.261-68; Moses (B.17.5-12) produces a letter patent which gives man the responsibility to fulfill the law of love.
Edwards, Art and Context in Late Medieval English Narrative. 37-50.