The master in this parable represents Father God who, at His own expense (the death of Jesus Christ), is willing to forgive all who cry to Him for mercy. A servant, who owed much, was forgiven but he was not thankful; instead he was very unkind to another servant who owed him money (Matthew 18:28-31). The outcry among the other servants was very great and the master called the first servant to deal with him.
 
The master appealed to the servant on the grounds of natural justice (what instinctively seems right or fair). He explained that he had cancelled the very large debt (10,000 bags of gold – Matthew 18:24) when the servant pleaded for mercy. He then told the servant that he should have also had mercy on the person who owed money to him. "Shouldn’t you …?" There was a moral obligation on the servant to release others from their debts: but he did not see that it applied to him.
 
The master was very angry; and rightly so. His generosity had not been received with thanks and the servant's greed increased. The threat of punishment had been removed but now the servant thought he could do whatever he liked and would get away with it. Even though the debt had been freely cancelled, the master still had the right to punish the servant for failing to accept the values of the household. Jesus said that Father God retains that right over all those who have benefited from His forgiveness but refuse to forgive others.
 
Forgiveness is part of the currency of God's kingdom. God exchanges our sin for His grace; all at great cost to Himself. He longs that all will repent and receive that grace which is freely available to all. However some will not care about building a relationship of love and thankfulness with God and will not want to own the values of His household/kingdom. The message for the disciples also applies to us. Unless we forgive those who sin against us, will not God take action against us? So the action should be clear: if we have received mercy, we must dispense mercy for Christ's sake.