Years ago I was being verbally and emotionally abused at the hands of basketball coach. I learned to hate him fiercely, and that carried over into anger and rage at life for many years. It was a bitter root within me that cost me much, and took years to deal with. I maintained a sarcastic, angry tone and voice for a long time afterwards, fueled by that bitter root.
Yet Hebrews 12:15 is clear to not let the root of bitterness spring up within us and defile many around us. It stains not only yourself but those you love.
Is there someone you hold bitterness against today, especially a brother or sister in Christ? Do you think you can contain that monster behind locked doors? It is not possible. It will leak out of you and cause casualties, for you and those you love. Hatred and bitterness cost me much before the Lord showed me a better way: forgiveness.
Years later that coach died of alcoholism and cancer, in a nasty way. But by then I did not rejoice over that, just a sorrow over his foolishness.
Do not let the root of bitterness grow within you! Confess it, and bring healing to your soul and mind. Forgive as Jesus forgave you. You are saving your own life from years of empty rage.