“Who is David? Who is the son of Jesse?” It is almost impossible that Nabal did not know about David—he would have known about him. David had been fighting the Philistines for years, was a commander in Saul’s army, and was the son-in-law of King Saul. Just from David’s killing of Goliath, David would have been known about around the kingdom. Also, Abigail, Nabal’s wife, knew all about David and that he was anointed to be the next king in Israel. So what we see in Nabal (“Mr. Fool”) is not ignorance, it is willful contempt. Nabal spurned God’s anointed ruler and would not help him in any way. Nabal thought he did not need God or His ruler.
It is also likely that what we see in Nabal is a willful blindness: he saw what he wanted to see. When he spoke about servants breaking away from their lords, he was referring to the way David was no longer with Saul, but Nabal turned a blind eye to why that occurred, which had nothing to do with sin or rebellion on David’s part. Also, the fact that King Saul was pursuing David deep into the wilderness to kill him showed that Saul had an intense interest in killing David, whereas he could have just dismissed him from service and let him go back to Bethlehem; so something was clearly wrong here. Furthermore, Nabal ignored not only the prophecies about David that Samuel had given that were likely well-known, but also ignored the ancient prophecy that the ruler of Israel would come out of the tribe of Judah. Nabal had no desire to submit to God or His anointed ruler, and so explained away his responsibility to do that.
This attitude of Nabal towards David is part of the scenario being set forth in the Bible of David being a type of Christ. Nabal is typical of people who are mean and selfish and who reject God and His Messiah, His anointed. They reject God because they are proud and arrogant and often think of themselves as self-sufficient, but like Nabal, their end will be death; death in this life and then everlasting death in the Lake of Fire.