Jesus gave strict instructions to "bless those who curse you, pray for those who mistreat you." (Luke 6:28). Doing such things is one way we step further into our true "sonship" in Jesus Christ. Understand, being born into God's family is a gift, but taking on his traits - such as forgiveness - is a choice. True forgiveness comes when we choose to give up our right to our feelings in exchange for the God's will in a given situation.
If you are harboring incomplete forgiveness (i.e., bitterness) you might want to consider the following:
1) Where would you be if God did not forgive you for some the things you've done, are doing, and will do?
2) What blessings of your own might you be blocking due to a lack of forgiveness?
3) What negative impact(s) is/are unforgiveness having on your life?
For me, the most profound notion that taught me to forgive is this: I was warring with myself, because my object had no idea how I was feeling. But whether covert or overt, unforgiveness hurts you more than the other person!
Before you decide to keep unforgiveness alive, ask yourself this:
Will this matter next year, next month, tomorrow, and above all, will it impact my eternity? If the answer is "No", you’ve got several reasons to let it go!