One of the most dangerous things a person can do is to hold onto resentment. Clinging to unforgiveness has far-reaching and often unexpected consequences.
Although bitterness takes root in the mind, it doesn't stay contained. Acrimony can spread into every aspect of a person's life. For example, the hostility a man feels toward his father can color his relationship with his wife, his willingness to perform at work, and his involvement in church.
It's probably not surprising to hear that resentment impacts the mind and spirit, but you may not have realized what a physical toll it can also take on us. An attitude of bitterness ratchets up tension and anxiety, which can affect everything from muscles to chemical balance in the brain. Over time, that kind of mayhem weakens the body.
Because unforgiveness is a violation of God's law, it also causes spiritual turmoil that hinders a believer's growth. Prayer is stifled because of harbored sin that should be confessed. And worship is dry and hypocritical because it's difficult to effectively honor the Lord while trying to justify or hide a wrong attitude. What's more, a resentful person's witness is damaged, as others are prevented from seeing God's glory shining through him.
Forgiving someone means giving up resentment and the right to get even with him or her, even though you were wronged. God insisted this was the only way to go through life. One reason He commands us to forego hostility and vengeance is that these things cause so much damage to our own lives.