Work at living in peace with everyone, and work at living a holy life, for those who are not holy will not see the Lord. Look after each other so that none of you fails to receive the grace of God. Watch out that no poisonous root of bitterness grows up to trouble you, corrupting many. Hebrews 12:14-15
Bitterness allows in unforgiveness. And if you refuse to forgive others, your Father will not forgive your sins. Matthew 6:15
Bitterness and unforgiveness leads to the desire to retaliate. But we must remember "Vengeance is mine; I will repay," saith the Lord. Romans 12:19
Bitterness, unforgiveness and the desire to retaliate allow anger and hatred to manifest.
Even now the ax of God's judgment is poised, ready to sever the roots of the trees. Yes, every tree that does not produce good fruit will be chopped down and thrown into the fire. Matthew 3:10
Sever any root of bitterness before it takes hold and produces the fruit of unforgiveness, anger and hatred.
R & K