I love talking about forgiveness, because God has forgiven me of so much over the years. I often think, how could I not forgive someone else when I have been forgiven so mercifully and graciously?
The life of every real Jesus-follower is a life of being forgiven and forgiving others. We are to confess our sins one to another, and then to forgive others if they sin against us. Forgive others, just as you have been forgiven.
To "forgive" mean: to cancel a debt. When you forgive someone you release them from any indebtedness towards you. That's what God has done, in Christ, for you. When you experience God's forgiveness, you don't need to pay anymore. The forgiven person goes free. God's forgiveness provides the ultimate "Get out of jail, free" card.
On the other hand, to withhold forgiveness is to say, "Let the punishment continue." To choose to not forgive someone for what they have done to you is to make the choice to make them continue paying. Unforgiveness locks the other person in the prison cell and throws away the key. If you refuse to forgive that person who has wounded you or stolen from you or done whatever to do, you administer 40 more lashes of the whip to their back, continuously.
Between forgiveness and unforgiveness there is no middle ground. It's always either freedom or bondage. Unforgiveness is not a "waiting" thing, like "You will someday face execution for what you have done." Unforgiveness straps the offender into the electric chair now and turns the dial to "high."
When you forgive someone, you set them free. They don't deserve it. But, and BTW, you don't deserve it either. So, because Jesus has forgiven you and released you from your indebtedness to him, who are you not forgive those who have set foot on your ground and violated you?
When you withhold forgiveness, it's not that you order someone else to be punished. You become the Punisher. That says something about you. About your heart. It's a dark heart, gripped by the accuser, that wants to do such a thing. It's a healed, forgiven, loved-and-loving heart that forgives and sets captives free.