Forgiveness is tough - as a general rule we aren't very good at it. We talk about it, we all want to be forgiven, but when it comes time to forgive others, when it is time to walk the talk, we don't do so well.
It isn't a new issue for us. There was a gentleman named Lamech mentioned in the 4th chapter of Genesis who had trouble with forgiveness as well.
Here's what he said about forgiveness - Gen 4:23-24 And Lamech said unto his wives, Adah and Zillah, Hear my voice; ye wives of Lamech, hearken unto my speech: for I have slain a man to my wounding, and a young man to my hurt. (24) If Cain shall be avenged sevenfold, truly Lamech seventy and sevenfold.
Some years later in Roman Palestine - a young Rabi was teaching his disciples and they asked him a question about forgiveness. He gave them this answer - Mat 18:21-22 Then came Peter to him, and said, Lord, how oft shall my brother sin against me, and I forgive him? till seven times? (22) Jesus saith unto him, I say not unto thee, Until seven times: but, Until seventy times seven.
Otto Koenig a missionary and christian speaker, talks about this verse and notes that 490 times gets him one and one third years. Actually, it's more complicated than that we should think of it as forgiving until the offense stops.
Almost nine years ago now the issue became a very important one for me. I was a victim of a terrorist attack. I lost some friends in the attack and I still have nightmares about the attack. However, because I call myself a Christian, it was necessary for me to deal with the desire for revenge and the anger that was caused by the incident. Part of the solution, is allowing G-d to be the ruler over my life. How successful I have been at that is an open question - some days I find myself praying that the leader of the terrorists will make a profession of faith in downtown Riyad. Other days I find myself thinking of the coals of fire - Rom 12:19-21 Dearly beloved, avenge not yourselves, but rather give place unto wrath: for it is written, Vengeance is mine; I will repay, saith the Lord. (20) Therefore if thine enemy hunger, feed him; if he thirst, give him drink: for in so doing thou shalt heap coals of fire on his head. (21) Be not overcome of evil, but overcome evil with good.
The only way that we can do that is to role model forgiveness to world that finds the concept to be totally alien.