Forgiveness is not always easy. The greater the hurt and sense of injustice, the larger the crime, the more difficult it is to forgive. The more we are required to forgive the same person, who then does the same thing again and again and again... it becomes harder to forgive.
Jesus tells a parable in Matthew 18:21-35 about two men. The first man owed a debt to the king of about £1.5 billion. How he managed to get in this situation is not important. What is important is that he could not repay the debt and yet the slate was wiped clean - he was forgiven.
The second man owed the first man a few thousand pounds (quite a lot if you have nothing, but not much in the context of 1.5 billion). Having just had his debt cancelled the first man came across the second man and demanded his money, and even though the second man pleaded for time, no mercy was shown, and the second man was thrown in prison.
When the king heard about this he was furious and had the first man thrown into prison until his debt could be paid.
A parable is a story with a point. So what's the point? We have been forgiven so much by God. And in the light of the way we have been treated by God we should show forgiveness to others. In Matthew 6:14-15 we see that Jesus teaches that our forgiveness from God is dependent on our having forgiven others.
It is important to note that this is not the same thing as letting someone get away with things over and over again. For within the context of Matthew 18 it is clear that sin needs to be dealt with (18:15-20).
