Forgiving others is very difficult for human beings. We are wounded through original sin, but we are made in the image and likeness of God, and God is merciful. St. Faustina has reminded us of divine mercy, and we are obligated to reflect that mercy to others.
Scripture is unequivocal about our need for mercy and the need for us to be merciful to others. The Gospel of Matthew is particularly good at this. "Then Peter came up and said to him, 'Lord, how often shall my brother sin against me, and I forgive him? As many as seven times?' Jesus said to him, 'I do not say to you seven times but seventy times seven'" (Matthew 18:21-22). Jesus then tells us a parable to help us understand the kingdom of heaven. It is the story of the king who forgives a servant who is in debt to him. The king forgives a huge debt (10,000 talents). The servant then shakes down another servant who owes him a much smaller debt (100 denarii), showing him no mercy. The king learns of this, and then says to him: "'You wicked servant! I forgave you all the debt because you besought me; and should not you have had mercy on your fellow servant, as I had mercy on you?" The servant is sent to prison "till he should pay all his debt. So also my heavenly Father will do to every one of you, if you do not forgive your brother from your heart" (Matthew 18:23-35). I have long found this passage very powerful. Because of the emphasis on forgiveness and the de-emphasis on money in this parable, I put a dollar bill at this passage in Bibles placed in hotel rooms I stay in. That's one way I try to quietly evangelize.
Earlier in the Gospel of Matthew we are told the connection directly between worship and forgiveness. "So if you are offering your gift at the altar, and there remember that your brother has something against you, leave your gift there before the altar and go; first be reconciled to your brother, and then come and offer your gift. Make friends quickly with your accuser, while you are going with him to court, lest your accuser hand you over to the judge, and the judge to the guard, and you be put in prison; truly, I say to you, you will never get out till you have paid the last penny" (Matthew 5:23-26).
Before we approach the altar to receive our Lord in the Eucharist, we say the prayer He taught us: the Our Father. We say: "forgive us our trespasses as we forgive those who trespass against us." If we do not forgive others, we are asking God to not forgive us.
How serious are we about that prayer? Are we as serious as Assunta Goretti, mother of St. Maria Goretti? In her excellent book, Real Saints, Real Women: Friends for your Spiritual Journey, Gina Loehr highlights the power of forgiveness in the story of the saint. Maria Goretti was only twelve years old when Alessandro Serenelli attempted to rape her. When she resisted, he stabbed her fourteen times. Maria lingered for a time afterwards; her mother, Assunta, was in the hospital with her until she died. As Loehr notes, Maria "declared that she had forgiven Alessandro and prayed that God would allow him to be with her in paradise. This perfect act of charity would inspire many others to forgive Alessandro as well. Assunta herself found courage to forgive the murderer because Maria had forgiven him first" (p. 66).
We evangelize by example.
This saint's forgiving heart changed Alessandro too. After eight years in prison, a glowing and angelic Maria appeared to him in a dream, offering forgiveness. From that time on Alessandro was repentant and remorseful. He served the remaining eighteen years of his sentence devoted to prayer and the sacraments" (p. 66).
Before we give up on people who we think are beyond redemption, we should recall Alessandro. After getting out of prison, he spent the rest of his life at a Capuchin monastery as a layman.
What truly impressed me about Assunta's story is this. She not only forgave Alessandro in her heart for killing her little girl, but she shared a heavenly meal with him:
On Christmas Eve of 1937, he came to seek forgiveness and to make what reparation he could. At midnight Mass he knelt beside Assunta as they both received Jesus in the Eucharist" (p. 67).
I do not know if I could find the courage to forgive someone for murdering my daughter, and then go to mass with that person. But that is what Jesus calls us to do, for that is what He did. "Father, forgive them; for they know not what they do" (Luke 23:34).