God is Ever Merciful and we always expect that He will deal mercifully with us and forgive our mistakes even if we falter again and again. But often we do not show mercy to others. There are instances which warrant clemency on our part but we choose to become callous instead. If a person commits a mistake accidentally or does so in ignorance and forgetfulness, we still scold and punish him. Similarly, at times, we become harsh and unforgiving even after a person has made amends and is genuinely sorry for his bad behaviour. Sometimes, we do not forgive a person even after we have taken revenge. At other times, we castigate someone for a small mistake or chide him much more than his mistake calls for. Similarly, at times, we adopt an unforgiving attitude towards a person who comes forward and confesses his mistake even before it comes to our notice. No doubt, all these are instances which warrant clemency and compassion from us. But we become callous, cruel and ruthless.
The Qur'an says that though a person can avenge the wrong inflicted on him by someone, yet forgiving and forgetting this wrong will earn great reward and indeed the pleasure of the Almighty.
Perhaps the most effective way to become a forgiving and forbearing person is to keep a constant and watchful eye on one's own faults and blemishes. We expect God and our fellow human beings to be magnanimous towards us by forgiving our faults. So we should be all the more ready to forgive the faults of others.
However, there can be instances which warrant an unforgiving attitude on our part. For example if a person is not sorry for his mistake and repeatedly commits the same mistake. Similarly, if a person does not realize his mistake and in fact shows arrogance in this regard, we need not show mercy or compassion. We may do likewise if a person continues to show carelessness and indifference in realizing that he has done something wrong.
Perhaps, the real test in this regard is to correctly and judiciously choose the instances which merit our forgiveness and those which do not.