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; that no one is sexually immoral or unholy like Esau, who sold his birthright for a single meal. Hebrews 12:15-16
Charismatic “inner healing” teaching majors on this “bitter root” doctrine. Typically, it’s said that the “seed of bitterness” is sown when some hurt happens to you, and instead of forgiving, you allow resentment to take hold in your heart. You have to go through healing to uproot this bitterness and negate the bad effects it has in your life. You’ll sometimes see even respected non-charismatic Bible teachers explaining the passage this way.
Hebrews 12, however, is not talking about the poison of bitterness in an individual person’s heart. To take it this way is to ignore two major rules of Bible interpretation: one, always look at context; and two, when a New Testament passage quotes the Old Testament, reading the OT passage often sheds light on what the NT author intended.
In this case, the original readers of the book of Hebrews, being Jewish converts to Christianity, would have immediately recognized this as a reference to Deuteronomy 29:
Beware lest there be among you a man or woman or clan or tribe whose heart is turning away today from the Lord our God to go and serve the gods of those nations. Beware lest there be among you a root bearing poisonous and bitter fruit, one who, when he hears the words of this sworn covenant, blesses himself in his heart, saying, ‘I shall be safe, though I walk in the stubbornness of my heart.’ This will lead to the sweeping away of moist and dry alike. Deuteronomy 29:18-19
So, the “root of bitterness” is a member of the covenant community who rebels against God, and secretly believes he will be exempt from God’s judgement despite clear warnings to the contrary. In the Old Testament, those warnings are the curses enumerated in Deuteronomy 28 for those who break the covenant. In the case of Hebrews 12, those warnings are the severe promises of judgement for anyone who rejects Jesus, scattered throughout the book of Hebrews.
Such a person’s rebellion has immense potential for destruction in the community, possibly influencing many to join them (“many being defiled”). This clause is part of a longer sentence; “see to it that no one fails to obtain the grace of God” and “that no one is sexually immoral or unholy like Esau” are further ways of expressing the same thought.
Hebrews 12 is not addressed to the individual believer but the church as a whole. It’s a warning about the necessity of dealing with sin and rebellion, not allowing it to grow and become a cancer that destroys many.
1 Corinthians 5 unpacks this teaching in much more detail. There, Paul writes to the Corinthian church about how to deal with a brother who has been caught in sexual immorality. The answer was to put him out of the church, and not to have anything to do with him or people like him who, while claiming to know God, indulge in serious sin. The reason, Paul says, is this:
Do you not know that a little leaven leavens the whole lump? Cleanse out the old leaven that you may be a new lump, as you really are unleavened. (1 Corinthians 5:6-7)
Leaven is a Biblical metaphor for sin. The sin of even one person, if allowed to grow unchecked, will work its way through the whole batch of dough (the church), to widespread destructive effect. This echoes what the writer to the Hebrews says about “many becoming defiled”.
To avoid this, church leaders need to be diligent about disciplining members who are caught and persist in unrepentant sin. They need to uproot that root before it grows, spreads, and chokes out the life of many surrounding plants (to extend the metaphor).