מלכים ב, פרק י׳, פסוק כ״ד

Jehu's carefully laid trap for the worshipers of Baal reaches its climax as the crowds gather for a grand celebration to perform their rituals. By actively participating in these sacrifices and burnt offerings, the worshipers commit an act of idol worship that is punishable by death. This provides Jehu with the legal justification needed to order their execution [מלבי״ם].

To guarantee that not a single person survives the ambush, Jehu stations eighty guards outside the building ahead of time. He issues a strict warning to these men regarding the worshipers placed under their direct watch and responsibility, making it clear that they must prevent anyone from fleeing [מצודת דוד, ביאור שטיינזלץ]. The primary approach among commentators is that the consequence for failure is absolute: if a guard is careless in his duty and allows a worshiper to escape, that guard will be put to death, paying with his own life in exchange for the life of the one who got away.