See to it that no one misses the grace of God and that no bitter root grows up to cause trouble and defile many. —Hebrews 12:15
Bitterness is an inward condition. It is an excessive desire for vengeance that comes from deep resentment. It heads the list of things that grieve the Spirit of God. (See Ephesians 4:30.) And it is one of the most frequent causes of people missing the grace of God. Bitterness will manifest itself in many ways—losing your temper, high blood pressure, irritability, sleeplessness, obsession with getting even, depression, isolation, a constant negative perspective, and generally feeling unwell.
We must, therefore, begin to get rid of a bitter and unforgiving spirit; otherwise, the attempt to forgive will fail. It is true that doing the right things, even when you don't feel like it, can eventually lead to having the right feelings. But the very act of trying to do right shows that the bitterness is not as deep as it could be. In other words, if someone feels bitter but begins to put the principle of total forgiveness into action, it shows that he or she is not totally controlled by bitterness. Otherwise he or she wouldn't make a start in doing what is right.
The absence of bitterness allows the Holy Spirit to be Himself in us. This means that I will become like Jesus. When the Spirit is grieved, I am left to myself, and I will struggle with emotions ranging from anger to fear. But when the Holy Spirit is not grieved, He is at home with me; He will begin to change me into the person He wants me to be, and I will be able to manifest the gentleness of the Spirit. Relinquishing bitterness is an open invitation for the Holy Spirit to give you His peace, His joy, and the knowledge of His will.
How can we be sure that there is no bitterness left in our hearts? Bitterness is gone when there is no desire to get even or punish the offender, when I do or say nothing that would hurt their reputation or future, and when I truly wish them well in all they seek to do.
Excerpted from Total Forgiveness (Charisma House, 2002).