How often does it happen that after we have a disagreement with someone and we have apologized and repented, that we still have lingering within us a seed of resentment? What happens when this is the case? The next time we run into conflict with them the old case rises again to make the current disturbance even worse. Or, when we hear someone else complain about this person, we are glad to hear this. Or, when we see something good happen to this person, we become upset to see them honored in such a way. This is all a case of rendering evil for evil.
Saint Dorotheos gives us an analogy:
A person lighting a fire first has a small piece of tinder. This represents the word of the brother who has upset him. This little fire is very feeble. What significance has the word of your bother? If you put up with it you blow out the small fire, but if you begin to think to yourself, "Why did he say that to me? I myself can answer him. If he did not want to hurt me, he wouldn't have said that and believe me, I can upset him too." In this case, you add small pieces of wood to the fire or some other fuel like the person that lights a fire and you produce smoke which is agitation.This hanging on to issues with lingering resentment is probably the greatest problem in all relationships, especially in marriages. We are not good at cleansing ourselves from the remnant of resentment. Even if we do repent and make amends we let hurts linger, only to have them rise up again and lead us to sin and turmoil.
How do we get rid of these remnants of resentment? Here is what Saint Dorotheos says,
By praying for the person that upset him, with his while heart, saying, "God help my brother (spouse) and through his prayers, me." Thus, he prays fervently for his brother (spouse), which is evidence of sympathy and love, and, at the same time, he humbles himself by asking for help through his brother's (spouse's) prayers. Where there is sympathy, love and humility how can anger, resentment or any other passion prevail?This is a common teaching of the Church Fathers. Evagrius writes, "The person that prays for his enemies has no resentment."
Try it. I think you will find that it makes a difference. In dealing with sin in our lives it is through the work of God's grace that we are healed. We only need to ask for it in our prayers.
Reference: Abba Dorotheos: Practical Teaching on the Christian Life, pp 153-158