KJV Below (NIV Link)
12 So speak ye, and so do, as they that shall be judged by the law of liberty.
13 For he shall have judgment without mercy, that hath shewed no mercy; and mercy rejoiceth against judgment.
The idea is not to act as though we are judged, but to act from the freedom given in Christ. The “law of liberty” is the covenant given in Jesus which is characterized by mercy. The reason mercy rejoices against judgment is that true mercy, real genuine mercy, is one that, when received, cannot help but pour it out to others. The reason the servant who is forgiven a debt and then demands a smaller payment is thrown in jail (a parable of Jesus), or that Christ prays we be forgiven as we forgive is not that we somehow earn the forgiveness, but that the evidence of having truly been forgiven, that is of truly taking the forgiveness to the core of our being as a new creation, is that we forgive others. If you are unable to forgive, you have yet to grasp the full measure of the forgiveness being offered to you. No, it’s not easy (no one said it was, in fact just the opposite), but when one accepts the forgiveness it is the only response left.
Do you have difficulty forgiving? What about when the other person doesn’t really care if you forgive them? Could the act of forgiving them actually make them change their heart and want to be repentant?