Matthew wrote his gospel for a Judaic audience. We know this for several reasons. The encounters between Jesus and the scribes and pharisees is apologetic, with Jesus defending his words in actions in light of tradition. Second, the Sermon on the Mount is an interpretation of Jewish law and tradition. Third, there are frequent references to Judaic Scripture in Matthew’s gospel.
One theme that recurs is the concept of forgiveness. In chapter 5, the Levitic prescript allowing “an eye for an eye” is upended: “But I say to you, offer no resistance to one who is evil.” Jesus teaches the crowd how to pray (6:9), saying “forgive us our debts as we for forgive our debtors.” Jesus elaborates further on this verse in the Lord’s Prayer in chapter 18.
Peter sets up the teachable opportunity, asking “Lord, how often must I forgive my brother?” (18:21). Jesus replies “seventy-seven times,” a reference and an offset to the seven-fold vengeance God would visit on a persecutor of Cain (Genesis 4:15) and the seventy-seven fold vengence on Lamech’s persecutors (Gen 4:24). In Genesis, we are warned not to seek revenge on those, like Cain and Lamech, who clearly do evil. Christ, says, in addition, that we are not merely to avoid revenge, but we are to forgive those who sin against us.
In order to emphasize the point, Jesus introduces the parable of the Wicked Servant at 18:23. In the parable, the master seizes a servant for failing to pay his debt, and the servant begs for mercy, which the master grants. The servant then seizes upon another and demands repayment for a smaller debt. The master, hearing of this, throws the “wicked servant” into prison until the whole debt is repaid.