There is a twisted part of us that enjoys the aftermath of people sinning against us. The thing that we enjoy is that being the victim carries with it an appearance of empowerment. It gives us license for self-righteous anger, and self-righteousness is a powerful drug.
(Believe it or not, Nietzsche said some very perceptive [even very Christian] things about this. Look up ressentiment on Wikipedia. No, I’m not going to link to Wikipedia.)
We can say all kinds of terrible things about someone who has sinned against us and not feel one bit guilty. Why? Because they sinned against us.
The hard part of forgiving people is that forgiving them means you have to stop beating them up (be it physically, psychically, or spiritually.)
If you forgive, then you are required to give up your superiority over them.
If you’re not willing to give up your superiority, then you’re not willing to forgive. Go back and read Matt 6.14-15 and Matt 18.35 again. (And again, and again, and again, …)
There’s a part of me that thinks that I don’t get to feel superior often enough. Convincing that part of me to give up the grudge I’m holding is a difficult thing. It’s like trying to take a bone away from a dog.