In the letter to the Hebrews, Paul talks to us about the priestly role of Christ. And in so doing he lectures us on forgiveness.
What? What does this have to do with forgiving others who have wronged us?
I mean, the guy who schmoozed his way into your promotion, the driver who cut you off in traffic, and the woman who slandered you at the last women's meeting have nothing to do with the priesthood of Christ. Or do they?
When any of these come to Christ, they have been forgiven by the One whose forgiveness is needful. They don't need our forgiveness. We need it.
"Their sins and lawless acts I will remember no more." (Jeremiah 31:34) If God remembers their sins no more, I need to forget as well.
There is an old hymn that says "Jesus paid it all." If Jesus paid it all, what more can I exact? I have no claim to expect additional recompense for a wrong. You see, He paid my "all" for me.
Since he also paid it all for the person who offended me, I need to recognize God's forgiveness of the offender and bring my will into line with His. Forgiveness is not a matter of emotions. It is a decision of the will.
Of course, once you have decided to forgive the offender, the enemy will be after your emotions. He'll try to stir up your anger and resentment. He'll play on your concept of fairplay. He'll do his best (worst) to get you to forget your decision and rely on your feelings. Don't fall for it.
When you have "decided to follow Jesus," you make your actions fit your decision. When you have decided to forgive, your hardest job will be reminding yourself of this decision each time the enemy tries to make you forget and feel.
Unforgiveness puts us at enmity with God, a state which I want no part of.