One of the hardest things to do is forgive our enemies. Jesus Christ has commanded us to turn the other cheek (see Matthew 5:38-42); however, it is all too easy to wish that those who have wronged us experience God’s wrath, or at least our own. But the Bible tells us that such anger and pain can hinder our relationship with God. As long as hatred and anger exist in our hearts, we cannot achieve the faith spoken of in the Gospel of Mark, namely, that we truly believe our prayers will be answered. It is only by recognizing the totality of Christ’s message of love — forgiving and loving our enemies — that we can achieve true closeness with God.
Taken from NIV Essentials of the Christian Faith