The root of bitterness always flowers into vindictiveness… And the only way to avoid bitterness is to practice forgiveness. Nothing else will uproot angry resentment.
How can we do this?
First, we have to realize what forgiveness is. Forgiveness is granted before it is felt (Luke 17:3-6). Forgiveness is primarily a promise to: not bring the wrong up with the person; not bring it up with others; and not bring it up in your own thoughts. It is a promise to not dwell on the hurt or nurse ill-will toward the other. These are under the control of your will. You are not able to keep a thought from occurring to you, but you don’t have to entertain it.
Second, we have to realize how forgiveness is possible: only because you see and feel the reality of God’s massive and costly forgiveness of us through Christ (Matthew 18:21-35). Only the knowledge of our debt to God can put into perspective someone else’s debt to us. The forgiveness of Christ gives us the emotional humility to forgive (Who am I to withhold forgiveness when I am such a sinner?) and emotional resources to forgive (What has this person really robbed me of, when I have so much in Christ?).
If with our hearts we dwell on Christ’s forgiveness of us, and with our wills we practice forgiveness of others, then slowly a feeling of forgiveness will come.
Lastly, we must forgive in our heats even before we try to be reconciled to someone who has done wrong (Mark 11:25). That way we won’t be too angry in our discussion with them and slip into trying to “score points” or to humiliate the person. In reconciliation we are trying to restore the relationship. We do that by admitting everything wrong we have done, by then pointing out any injustice that they have done, and then asking to be reconciled.
From Judges For You by Timothy Keller, pp 191-192.