Anger forgets. Anger feels justified, after all, this is why we are angry. In our minds our standard has not been met. Our expectations have been ignored. Our sense of right has been violated. Those who have failed need to understand that our will has been thwarted and this behavior is unacceptable. They deserve to feel our anger!
But anger forgets! It forgets that our standard is not the expectation. More importantly, it forgets that we have been shown great grace. Jesus tells a parable in Matthew 18:21-35. The account shows a king who is owed a huge debt by one of his servants. The debt is equivalent to the total income of several lifetimes of work. In other words, it is a debt that could never be paid. The servant pleads for leniency, but the king does more and forgives the whole debt. He does not give more time, but rather he removes the debt.
This same servant is seen later that same day confronting a fellow servant in anger because he is owed a small debt (one-days wage). This servant that was just forgiven so much refuses to extend forgiveness, but responds in anger and throws the debtor in prison until the debt is paid.
The application is clear. We have been forgiven a great debt that is beyond our ability. We have received grace in place of wrath that we rightly deserve. Yet in our anger, we penalize and throw others into figurative prisons for failing to meet our expectations. We refuse to share even the smallest portion of grace that we have received in abundance. This is sinful and violates the grace of God. This elevates our standard beyond the grace we have received from God.
In anger we forget the grace we have received. We have received much grace from God. This frees us to give much grace to others rather than responding in anger.