Summary: After the victory at Jericho, Joshua leads the people to their second conquest against the city of Ai. A relatively small army is sent to attack but is defeated. Joshua prays and is answered by God explaining that the nation has sinned. In fact, only one Jew sinned by removing consecrated property. The offender, Achan ben Karmi is discovered through a lottery and punished accordingly. After planning a rear attack on the city, the people succeed in capturing Ai. The recitation of the blessings and curses on mount Eival and Mount Gerizim, commanded in Deuteronomy chapter 27 is recounted.
A deeper look: During the conquest for Jericho, the people were commanded to resist the temptation to pilfer the many riches of the city. Out the entire nation of 3 million, only one individual succumbed to human frailty. Nevertheless, given the exceedingly high standards expected from the Jewish nation coupled with the principle of כל ישראל ערבים זה לזה– that the Jewish people are intrinsically bound together, the effect of one person’s sin degraded the stature of the entire people.
The nation had been promised God’s protection in their conquest for the land. Yet it was now clear this was unambiguously contingent on their conduct. Whereas the first army to attack Ai was only 3,000 strong, Joshua now assembled his soldiers in full force and devised a complex rear end attack on the city to ensure victory.
One might ask why such plans were necessary. God had assured the people of victory and explained the reason for defeat at the first attempt on Ai. Surely such a display of force could jeopardise the people’s belief that it was only God’s Divine assistance which could assure victory.
Rabbi Shmuel Bornsztain (d. 1926, known as the Shem MiShmuel) explains that Joshua did not muster such force out of fear of defeat. In the aftermath of defeat, Joshua included the entire military might of the people to rebuild morale through the unity of the people. The message was, and still is clear; the Jewish nation is like one being and when our hearts beat as one, we can overcome the greatest foes.