Hebrews 12:15 describes bitterness using botanical language: "lest any root of bitterness springing up trouble you, and thereby many be defiled." The Greek riza — root — operates underground, invisible, before it produces visible damage. The warning is not against experiencing bitterness but against allowing it to root in a way that spreads its contamination into other relationships and areas. Roots grow when they are not addressed. Addressed bitterness does not become a root.
Ephesians 4:31–32 lists bitterness alongside wrath, anger, clamour, and evil speaking — all things to be "put away." The Greek airo — "put away" — means to lift up and carry off, to remove entirely. This is not suppression but active removal. The path through bitterness in Paul's framework is not denial of the wrong but its replacement: "forgiving one another, even as God for Christ's sake hath forgiven you." Forgiveness is possible because it does not require pretending the wrong was acceptable.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.