Letting go of anger and negativity in your heart is like opening up an old chest to find dust and dead bugs in it. You and others become disgusted by it and don’t want to deal with it, but it has to be cleaned up and rid of it’s filth in order to restore that which is pleasant.
(Mark 11:25-26) 25 “And whenever you stand praying, if you have anything against anyone, forgive him, that your Father in heaven may also forgive you your trespasses. 26 But if you do not forgive, neither will your Father in heaven forgive your trespasses.”
(Hebrews 12:14-15) 14 Pursue peace with all people, and holiness, without which no one will see the Lord: 15 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;