Perplexing Parable of the Unjust Servant

Considering v1-13 in the context of v14-18, the parable is about the Pharisaical misinterpretation and mishandling of God's Word.

Master / Rich Man = God
Steward / Manager = Pharisees
Debts = Word of God
Debtors = Recipients of God's Word

The Pharisees took God's revelation, diminished and twisted the meaning and requirements to make them attainable and so to justify themselves. Jesus provides the example of their misinterpretation by citing the divorce laws in v18.