2nd Samuel chapter 3.
The commander of Israel's army, Abner, seems to have had a change of heart against Israel and for David's kingship. As a result he helped King David gain support from other tribes. David's Commander, Joab, was very bitter and hateful toward Abner because Abner had killed Joab's brother in the past. Even though Abner did not want to kill Joab's brother, Joab was very bitter towards Abner. As a result Joab and his other brother killed Abner.
Bitterness and unforgiveness is the fruit of hate which results into destruction. It is within us to want to get revenge. People kill people for their wrongdoing and their mindset is, “They deserve it.”
If God operated toward us the way we operate toward others then we also deserve death for our wrongdoings daily against the Lord. But rather God has shown us mercy and grace through a relationship with Jesus. He loves and forgives us rather than retaliate, hate or show unforgiveness. Therefore let us seek to love and forgive others which is the best approach especially if you want to win someone over to the Lord.