Forgiveness, he says, is not to be a replacement for judgment. It is something else entirely. It is meant to change us and the whole community in which we live. The king's action failed to affect the man in the way it was intended and he did not respond in a like manner to his debtors, so he ended up being treated according to the old justice system. The intent of forgiveness is to change the heart and the whole way of being one with another.
Forgiveness is tough to accomplish.
It is actually counter-cultural. Just read the newspaper with the idea of forgiveness in mind. Many of the articles have to do with holding people accountable, establishing blame, and getting those scales even again. Forgiveness seeks another way. The king does not say that.