There’s a natural spring that rises on the east side of the city of Jerusalem. In ancient times it was the city’s only water supply and was located outside the walls. Thus it was the point of Jerusalem’s greatest vulnerability. The exposed spring meant that the city, otherwise impenetrable, could be forced to surrender if an attacker were to divert or dam the spring.

King Hezekiah addressed this weakness by driving a tunnel through 1,750 feet of solid rock from the spring into the city where it flowed into the “Lower Pool” (2 Kings 20:20; 2 Chronicles 32:2–4). But in all of…