He has offered me an outrageous insult, you say. He has wronged me times without number, he has endangered my life. Well, what is that? He has not yet crucified you as the Jewish elders crucified the Lord. If you refuse to forgive your neighbor's offense your heavenly Father will not forgive your sins either. What does your conscience say when you repeat the words: “Our Father who art in heaven, hallowed be thy name,” and the rest?
Christ went so far as to offer his blood for the salvation of those who shed it. What could you do that would equal that? If you refuse to forgive your enemy you harm not him but yourself. You have indeed harmed him frequently in this present life, but you have earned for yourself eternal punishment on the day of judgment. There is no one God detests and repudiates more than the person who bears a grudge, whose heart is filled with anger, whose soul is seething with rage.
Listen to the Lord's words: “If you are bringing your gift to the altar, and there remember that your brother or sister has something against you, leave your gift there before the altar and first go and be reconciled. Then come and offer your gift.” (Matthew 5:23-24)
What do you mean? Am I really to leave my gift, my offering there? Yes, he says, because this sacrifice is offered in order that you may live in peace with your neighbor. If then the attainment of peace with your neighbor is the object of the sacrifice and you fail to make peace, even if you share in the sacrifice your lack of peace will make this sharing fruitless. Before all else therefore make peace, for the sake of which the sacrifice is offered. Then you will really benefit from it.
The reason the Son of God came into the world was to reconcile the human race with the Father. As Paul says: “Now he has reconciled all things to himself, destroying enmity in himself by the cross.” Consequently, as well as coming himself to make peace he also calls us blessed if we do the same, and shares his title with us. “Blessed are the peacemakers, he says, for they shall be called children of God.” (Matthew 5:9)
So as far as a human being can, you must do what Christ the Son of God did, and become a promoter of peace both for yourself and for your neighbor. Christ calls the peacemaker a child of God. The only good deed he mentions as essential at the time of sacrifice is reconciliation with one's brother or sister. This shows that of all the virtues the most important is love.
St. John Chrysostom, c. 347-407
But all things are of God, who has reconciled us to himself by Christ;
and has given to us the ministry of reconciliation.
~2 Corinthians 5:18