I can't think of anything more damaging to the soul than the root of bitterness. Every one of us has been hurt by another member of the human race. Most of us have multiple wounds that fester inside of us. We often underestimate how damaging bitterness can be to our souls.
God offers the only alternative to bitterness and that is forgiveness and trusting Him with revenge for what was done to us. At first glance this might appear to be a thoughtless gesture to overcome the horrid result of someone else’s sin against us. How could forgiving that awful person bring us any kind of peace? But once you've obeyed God and experienced the healing power of forgiveness, you will understand.
David knew the power of forgiveness and trusting in God to avenge those who sin against us first hand. Although a great leader and called a friend of God, David also had his failures. Through those times of failure, David learned the secret of overcoming disappointment and bitterness. The secret was forgiving that person through the power of God (He didn't even know the full expression of God’s forgiveness through Christ as we do.) and not seeking revenge!
David clearly displays the attitude God can work with when we are in the trench of bitterness. In 2 Samuel 16:5-14, we find David as the target of unfair criticism. Shimei, a man from Saul’s clan, curses David and throws rocks at the King of Israel. David’s associates are enraged at the thought of this man’s actions and asked David if they could go and cut off the man’s head (2 Samuel 16:9). David’s response totally surprises me and everyone who reads this passage. He chooses to leave this man in God’s hands. Rather than take his own revenge (as he could easily do), he believes that God could be working through this man to remind David of his humble estate. David wants to practice forgiveness and trusts God to seek revenge at the proper time because He believes God knows better than he. David is the victim of cursing by this man, and the victim of stones thrown at him, but he is not the victim of bitterness. Bitterness has not taken David captive and rendered him powerless as a servant of God.
If you read the story in context, you will also note that this incident happens in the midst of David’s son Absalom’s rebellion against him. David was able to overcome these great acts of disrespect and disregard against him through clinging to God for the right perspective. It is only natural for people to defend when attacked. David’s associates were so angry they wanted to cut off the head of the man who disrespected David so. It is natural to seek revenge and fill up with bitterness, but that only gives Satan room to work in your life. It takes getting rid of bitterness to leave room for God to overcome the horrible act of sin against you. Ephesians 4:26-27 says, In your anger do not sin. Do not let the sun go down while you are still angry and do not give the devil a foothold.