Capturing a strategic target often requires a powerful motivation for the fighters. To secure a crucial victory, Caleb presents a highly personal reward, offering his own daughter, Achsah, in marriage to the warrior who successfully conquers Kiryat Sefer. This public promise serves as a strong incentive to drive a capable fighter to step forward and complete the mission.
Although Kiryat Sefer is not a particularly large city, it holds significant importance. The need for such a unique prize points to an underlying military challenge. It is likely that Caleb was struggling to gather and organize his army on his own for this battle. By putting forward such a valuable reward, he guarantees that the necessary forces are rallied to achieve the conquest.