" David had every right to be angry and take vengeance upon such a character as Nabal, who insulted him and his men, yet God had something different in mind. In Romans 12 verse 19 we read that it is God who will avenge, He will repay. It is not our job. And God knows exactly how to get through to people.
God had a very specific purpose in this whole event – He was getting David ready to move into kingship and David had some character building left to do which he did by giving heed to Abigail’s words of wisdom. Abigail, in wisdom, asked for forgiveness from David for her husband’s foolish words but she also appealed to him to be gracious to her and her household while reminding him of what God had promised to David regarding his future as leader of Israel. God was busy softening David’s hear. This was a lesson in grace. David learned how to show the grace of God to Abigail. "

― Paddick Van Zyl