Hebrews 12:15 says, “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 people become defiled.”
I sometimes hear this verse referenced as a warning against harboring bitterness or a grudge against someone. It is an easy assumption to make since we tend to read the Bible very individualistically. We sometimes treat it like a private devotional rather than what it actually is, a public word to the assembly of God’s people.
And harboring bitterness or a grudge against someone is bad, but that is not what this verse is talking about. This is not a warning about an attitude that anyone is susceptible to, but a warning about a person in the congregation who is a corrupting influence.
There is no translation problem, but it is easy to overlook the fact that the ESV (correctly) has “root of bitterness” in quotation marks. This is because the author of Hebrews is alluding to Deuteronomy 29:18-19, which says:
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 the 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.
So a “root of bitterness” is not an attitude, but a person who is presumptuous and flatters themselves in their sin, one who hears the word of God but shrugs it off as inapplicable to him or herself. This kind of person is a danger to the whole church, and can bring about the defiling of many. This interpretation makes sense in the wider context of Hebrews 12:12-17, which speaks of possible types of individuals among the assembly: One who might fail to obtain the grace of God (v. 15) or one who is sexually immoral (v.16). The “root of bitterness” is another such person, who will bear poisonous fruit.
This person is someone like what the church of Thyatira is warned about in Revelation 2:18ff, a church that was tolerating “that woman Jezebel” who through false teaching was seducing the people of God into sexual immorality and subtle idolatry.