The answer is: He had blasphemed against God and the king

1 Ki 21

The story of Naboth's vineyard is laden with lessons on injustice, greed, and power dynamics. Naboth was just a simple man, blessed with a vineyard that stood in stark contrast to King Ahab's desires. The sweet fruits of Naboth's land served not just as a menu item but as his ancestral inheritance—a strong connection to his roots. When Ahab sought to possess the field, Naboth bravely declared that it would be wrong to part with what was rightfully his. So far, so good; we see moral fortitude.

But the plot thickens! Inspired by Ahab's covetousness, Queen Jezebel devised a nefarious plan that involved crafting falsehoods. She capitalized on Naboth's piety, branding him a blasphemer—a punishing label that carried immediate death. This signals the danger of tempting opulence and the lengths to which some will go to secure their desires.

Interestingly, one might recall the Kingdom of Israel's previous kings, as their reigns often flickered greedily with corruption and concentrated power. Ahab and Jezebel in their plotting mirror a long line of leadership obsessively chasing their ambitions, often highlights of the ongoing human struggle between influence and integrity.

This event resonates well beyond its historical context; echoes of deceit for personal gain can resonate in many facets of society today, making us ponder our values and priorities. Naboth’s courage reminds us of the steadfastness in holding on to what is just, confronting lies even when faced with powerful opposition. Such biblical stories ignite important discussions around ethics and morality even now.