David heard in the wilderness that Nabal was shearing his sheep.
The Old Testament prophets regarded those who are ungodly, namely, those who do not take God into account, as fools (Psalms 14:1; Proverbs 18:2; Proverbs 18:7; Isaiah 32:6). God promised to punish the ungodly (Deuteronomy 28), and He will punish fools (1 Samuel 25:25-26).