Another person has wronged you and hurt you, or you believe that he has, and so you store up bitterness in your heart. But this bitterness pollutes and eats away at your own soul, not the soul of the one who wronged you.
What this means is that someone came into your home and smashed your precious things. And let us say that you are not imagining it—he really did this. And so what does bitterness do? Bitterness goes to the workroom in the basement, finds a hammer, and goes through the house, smashing any of the remaining precious things that the other may have missed. At the basic heart level, this means that bitterness agrees with the vandal. For all the appearance of conflict, it is a false conflict.
Aggressive belligerence says that you should be hurt. And bitterness responds by saying, "No, I need to be hurt and damaged more than that. Leave me now—I can do the rest by myself."
The author of Hebrews says not to let the root of bitterness spring up, defiling many. And when this happens, the people involved fall short of the grace of God (Heb. 12:15). But we must remember that the Old Testament associates the bitter root with the sin of idolatry. When we are resentful, more is involved than just a "cranked attitude." We are no longer worshipping the loving Father who controls all things perfectly, including this situation, for His glory and our good. And this means that, in our bitterness, we are trying to appease an idol, a deity who cannot deliver us.
It works the other way too. When we turn aside to false gods, whether they are the gods of sex, money, ambition, the end of that road is bitter, bitter destruction. This is a two-way street. Bitterness leads straight into idolatry, and idolatry leads straight into bitterness.
If you are anywhere on that road, if you are bitter, if you are idolatrously chasing other baubles, there is only one thing to do. Turn around and walk the other way.-Douglas Wilson