The passage in question reads in full, beginning in verse 14:
“Pursue peace with all people, and holiness, without which no one will see the Lord: looking carefully lest anyone fall short of the grace of God; lest any root of bitterness springing up cause trouble, and by this many become defiled; lest there be any fornicator or profane person like Esau, who for one morsel of food sold his birthright. For you know that afterward, when he wanted to inherit the blessing, he was rejected… (verses 14-17).”
Paul gives us several examples to avoid, in order to make sure that we will inherit the blessing of the Kingdom of God. He tells us that if we don’t pursue peace with all people, but rather continue to live a contentious life style, we will not see or be accepted by Jesus Christ. The same is true when we don’t live holy or God-pleasing lives. He also explains that we won’t inherit the blessing either, when we allow a root of bitterness to spring up causing trouble; and finally, we won’t be accepted by God if we commit spiritual fornication by rejecting, through our words, thoughts and deeds, the gift of eternal life which God has in store for us.
Especially the term, “root of bitterness,” is very meaningful, as it can and will defile the bitter person, as well as others, if it is not immediately rooted out.
The Broadman Bible Commentary explains:
“It is interesting to observe that this… [phrase] (‘root of bitterness’) was used by Peter in his denunciation of Simon Magus, who tried to buy the gift of the Holy Spirit with money (Acts 8:23). The writer may be referring to the passage in Deuteronomy 29:18: ‘Beware… lest there be among you a root bearing poisonous and bitter fruit.’ Here the warning is against one who assures himself that he is in the covenant relationship, even though he continues to keep a stubborn heart.”
The Commentary continues to point out that Hebrews is referring to “those people who are like Esau, who value immediate gratification of sensual desire above the final approval of God.”
The Commentary on the Whole Bible, by Jamieson, Fausset and Brown, explains that the root of bitterness “comprehends every person and every principle of doctrine or practice so radically corrupt as to spread corruption all around. The only safety is in rooting out such a root of bitterness… So long as it is hidden under the earth it cannot be remedied, but when it ‘springs up,’ it must be dealt with boldly.”
The New Bible Commentary:Revised adds that a person with a root of bitterness “can bring defilement on the whole congregation.” It refers in this context to the story of Achan, in Joshua 6:18; and 7:25.
When checking the Greek word for “bitterness,” i.e., pikria, it is defined, by W.E. Vine, Expository Dictionary of New Testament Words, as “denot[ing] bitterness.” The Dictionary continues to point out that it “is used in Acts 8:23, metaphorically, of a condition of extreme wickedness, ‘gall of bitterness’ or ‘bitter gall’; in Rom. 3:14 of evil speaking; in Eph. 4:31, of bitter hatred; in Heb. 12:15, in the same sense, metaphorically, of a root of bitterness, producing bitter fruit.”
We can see, then, from the forgoing that the springing up of a root of bitterness must be avoided at all costs. This root does not suddenly appear, without having first been nurtured in the heart of a person. We see from the Biblical examples that the root of bitterness can be the result of wrong motives, thoughts, desires and actions. It is therefore important that we examine our hearts, to see whether Jesus Christ lives in us (compare 2 Corinthians 13:5), or whether we have a bitter, hateful, stubborn or hardened heart and a contentious spirit. If we do have such an arrogant heart (compare Isaiah 9:9), we must repent of it immediately, purify our hearts (James 4:8), and ask God to give us a humble and submissive heart (Matthew 11:29).