“See to it that no one fails to obtain the grace of God; that no ‘root of bitterness’ springs up and causes trouble, and by it many become defiled,” (Heb. 12:15).
The theme and backdrop for the book of Hebrews is a warning to Jewish Christians against turning back to the old ways of Judaism. The message is, Christ is here now, serve Him.
The bitterness of this text is most likely associated with Deut. 29:18. The Israelites came out of Egypt by God’s power under the leadership of Moses. But as they were taken out of slavery to freedom and ultimately to the promised land – they complained and became bitter against their leaders and God. Forgetting about the good life in Canaan that lay ahead of them, they murmured, rebelled, and therefore, failed to obtain the grace of God (that is, a whole generation missed out of the promised land).
Thus, Heb. 12:15 becomes a warning to us. God, through Christ, has taken us out of the slavery of sin and has promised us the “promised land” of heaven. Complaining, murmuring and rebelling will gradually defeat us. It is like a bad root that eventually emerges and poisons others.
There is another context of bitterness referred to in Eph. 4:31. The bitterness of that verse has more to do with resentment toward people, holding grudges, harboring hostility, or smoldering resentment toward people – that has no spiritual value and helps nobody. Often, this bitterness toward people hurts the one who is bitter more than anyone else.
In his commentary on the Greek text, John Eadie puts it best: “Bitterness is a figurative term denoting that fretted and irritable state of mind that keeps a man in perpetual animosity—that inclines him to harsh and uncharitable opinions of men and things—that makes him sour, crabbed, and repulsive in his general demeanor—that brings a scowl on his face, and infuses venom into the words of his tongue.”