The results of unforgiveness are among the worst suffering, if not the worst emotional suffering, you can possibly experience on earth. It is a foretaste of Hell and of the judgment of God. The Bible tells you (https://www.biblegateway.com/passage/?search=Matthew+18%3A21-35&version=NKJV) that if you do not forgive, God Himself will send torturers upon you. These torturers do not wear a black hood and carry you to a dungeon. The torturers are resentment, fear, pain, despair, insanity, suicidal depression, excruciating agony, “mental illness” and suffering that is far beyond what most people who have not experienced it believe is possible.
The difficulty with this and the reason it is so tempting to not forgive is that people feel so absolutely justified in hating and resenting people who have egregiously and with full will caused them so much intense, excruciating, unimaginable, and long-lasting suffering, sometimes lasting decades, as, for example, the suffering that results from childhood abuse, whether it be sexual, violent, or psychological.
And yet forgiveness is the only way out of this hell on earth.
If people cannot forgive, they need to ask God, in Jesus’ Spirit, to help them forgive.
If you do not forgive, your suffering here will never end, and if you are an unbeliever, your suffering will never end, even in eternity.
It seems so damned unfair to first suffer excruciatingly from the sins of others perpetrated on us, whether sexual abuse or violent abuse or emotional abuse, and then to have to suffer again, even more intensely, from the results of not forgiving what was perpetrated against us.
But if you do not forgive, your suffering here will never end, and if you are an unbeliever, your suffering will not end, even after you die.
When we forgive, our intense suffering alleviates and disappears immediately.
But forgiveness is also a repetitive process: resentment and pain can return again and again if even a shred of unforgiveness persists against anyone, for anything.