The answer is: Achan

Josh 7:1 - Achan's sin was the cause of the defeat at Ai resulting in 36 Israelites being killed in the battle.

Achan's story unfolds a dramatic twist right after the jubilant fall of Jericho, a moment that could make any warrior's heart swell with pride. The Israelites had just witnessed the miraculous collapse of Fort Jericho's walls, yet in their first taste of conquest, one man's selfish act turned their victory into defeat. Achan's ambition stands in stark contrast to the communal principle emphasized throughout the narrative: everything in Jericho was to belong to God.

His choice to seize a beautiful cloak, silver, and gold is like a cautionary tale echoing throughout Scripture. The concept of 'herem' or 'the ban' illustrates that some objects—notably those diametrically opposite to spiritual values—are best left untouched. It shows the two faces of faith: while trust can lead a community to overwhelming victory, individual failure can reverberate tragically.

This incident reverberates beyond Joshua, as it establishes a significant theme of collective accountability. Everyone is affected by one person’s departure from God’s commands—a thread woven into both the Old and New Testament ethos. Think of how the act of one, like Judas Iscariot, can sting the collective community even centuries later!

Interestingly, archeological evidence from ancient Jericho shows no signs of a destruction layer dated to Joshua's time, local scholars debate whether these accounts should be taken literally. So whether we see it historically or mythically, Achan's story serves as a profound reminder of the importance of faithfulness—not just to oneself, but for the community. This makes us think about our values and choices, since they define the world around us.