Viewed from a vibrational perspective, living with resentment keeps us from resonating at the higher levels of joy, gratitude, and enthusiasm. It keeps our physical and emotional state of being at the lower levels and tends to isolate us from awareness of spiritual community. There is always a payoff for what we do, and the payoff for holding resentments is that we get to be right, something that the unconscious mind holds in high esteem. Resentment (being a product of the ego rather than the soul) puts us in the position of a victim, a persecuting judge, a martyr, or a righteously angry person... all roles of separateness rather than connection.
Given that resentments are lonely burdens to carry, what can we do with them? Acknowledgement is a good place to start and it can be helpful to diagram them from the point of origin. Begin with defining your resentment on paper in the center of a page. Above it on the left side write what you are angry about, and on the right side what your fears are with regard to this resentment. Then, beneath your resentment, on the left side write what the other person did and then what you think the other person should have done. And then, on the right side, write about what you did and what think you should have done.
Then ask yourself some questions: Were my feelings justified? Even if your feelings were totally valid at the time of the event, carrying them around months or years later is probably not in your best interest. Did the other person do what I wanted them to do? Probably not. Did I do what I think I should have done? Unlikely, but even if your resentment puts the onus on the other, do you really want to continue to carry these negative repetitive thoughts?
If we look at the diagram of the resentment we can see that it is wired around the belief that a person, place or thing should not be the way that they are, that things should not have happened the way they happened. So the opposite of resentment is really just acceptance of people places and things for who and what they are (or were). As Byron Katie says, "When you argue with reality, you always lose'. Acceptance of what happened doesn't necessarily mean that we like it or agree with it; it just means we concur that it happened and acknowledge what is beyond our control. We chose to focus instead on what we can control: our beliefs and choices and how we live today. And once we come to a place of acceptance we may then begin to contemplate the words of Stephen King in his book The Wind Through the Keyhole: "The two most beautiful words in any language are 'I forgive'". Ah, but that is another tidbit.