Grudges are not only harmful to one’s physical health, but also to one’s spiritual health. A grudge is an attitude of unforgiven, which comes from a belief that the other person is undeserving of being released through YOUR forgiveness (like as if you have that authority).
“They deserve to suffer” is what you say. But in reality, everyone suffers; the person that doesn’t forgive, the unforgiven person, and the people who know both parties.
This is what Pastor Greg Laurie of Harvest Christian Fellowship had to say in his book “Discipleship“:
“If you have really been forgiven [by God], and you understand something of that forgiveness, you will be forgiving to other people. If you are not forgiving to other people, I question whether you know any thing of God’s forgiveness in your own life.
A forgiven person will be a forgiving person. A true disciple will harbor no grudge in his life toward another. The disciple knows it will hinder his prayer life and his walk with God. Let’s not forget what Jesus said, “By this all will know that you are My disciples, if you have love for one another” (John 13:35).
For that reason, no child of God can walk around with bitterness, anger or hostility in his heart toward another person without feeling the conviction of his sin. “We must forgive others as we have been forgiven.”
See also: Psalm 66:18; 1 John 1:9