So if you are presenting a sacrifice at the altar in the Temple and you suddenly remember that someone has something against you, leave your sacrifice there at the altar. Go and be reconciled to that person. Then come and offer your sacrifice to God. - Matthew 5:23–24
An unforgiving Christian is an oxymoron. If you are a Christian, then you must forgive, because forgiven people are forgiving people. Therefore, you cannot be an unforgiving Christian. And if you want your prayers to be answered in the affirmative, then you must forgive others. Jesus gave this command: "If you are presenting a sacrifice at the altar in the Temple and you suddenly remember that someone has something against you, leave your sacrifice there at the altar. Go and be reconciled to that person. Then come and offer your sacrifice to God" (Matthew 5:23–24).
Jesus also taught us to pray, "And forgive us our sins, as we forgive those who sin against us . . . (Luke 11:4). We need to learn to forgive, because we are all flawed. We will sin against people, and people will sin against us. Husbands will offend their wives, and wives will offend their husbands. Parents will offend their children, and children will offend their parents. Family members will offend one another. Friends will offend one another. So we must choose to forgive. We must determine not to let those offenses keep us from communion and fellowship with God.
It may be that someone has really hurt you. You may even have every right to be angry and bitter. But do you know who gets hurt the most when you harbor anger and hostility and vengeful thoughts toward someone? You do. And not only that, you are cutting yourself off from fellowship with God. Ephesians 4:32 tells us to "be kind to each other, tenderhearted, forgiving one another. . . ."
When God forgave you, did you deserve to be forgiven? Does the person who hurt you deserve to be forgiven? Forgive anyway. Based on God's love and grace, we should forgive.