Where there is anger, the peace of God cannot be present. Which do you prefer --- His peace or to be righteous and stay in your anger? If you choose His peace, the only path out of the anger is forgiveness --- forgiveness of that person, that group, yourself, the world, and often forgiveness of Him. Why do we need to forgive God? Because we believe that he has done something (an action) or not done something (not delivered us) which has created the situation we are in, the illness that afflicts us, etc. But this is false.