The first battle of the Israelites against their enemy unfolds across two parallel fronts. While a visible, physical clash takes place on the battlefield below, a hidden, spiritual struggle is waged on the mountaintop above through prayer [מלבי״ם]. Joshua carries out his orders, selecting men and marching out to fight the enemy directly [שד״ל, קאסוטו]. At the same time, Moses, Aaron, and Hur ascend the mountain to fast, repent, and pray for the nation's survival [צאינה וראינה]. The presence of Aaron and Hur sets the stage for the unfolding conflict, as they will soon need to physically support Moses [אבן עזרא, חזקוני, ביאור יש״ר, שטיינזלץ].
The gathering of these three leaders establishes a foundation for the practice that during a public fast, three people are required to lead the community in prayer [רש״י, העמק דבר]. Moses stands in the center, with Aaron and Hur positioned on either side to assist him, much like elders who support a community prayer leader [מלבי״ם]. This moment also marks the first appearance of Hur in the biblical narrative [קאסוטו, ברכת אשר על התורה]. The primary approach among commentators is that Hur is the son of Miriam and Caleb [רש״י, דעת זקנים], though a historical tradition suggests he is actually Miriam's husband [שד״ל].
His selection to join Moses and Aaron is deeply intentional. The Israelites are guided by three shepherds: Moses, Aaron, and Miriam. In a time of severe danger, the merit of all three is required to save the nation. Because it is not customary for a woman to stand alongside men in public prayer, Hur is chosen to represent his mother, bringing Miriam's protective merit with him to the mountain [גור אריה, ברכת אשר על התורה]. The location itself holds symbolic weight. Reaching the top of the hill invokes the protective merit of the Patriarchs, while the hill itself represents the merit of the Matriarchs, both of which stand by the Israelites in battle [דעת זקנים].
Moses understands that raising his hands carries a critical psychological and spiritual impact on the warriors below. As long as his hands are raised, the Israelites are filled with courage and overpower their enemy. If he lowers them, the fighters will retreat and the enemy will prevail. He brings Aaron and Hur specifically to ensure his hands remain raised and steady throughout the conflict [בכור שור]. However, Moses' hands eventually grow heavy, requiring this physical support. Some suggest this fatigue is a consequence of a misstep, as Moses sends Joshua to fight in his place rather than going down to the battlefield himself [צאינה וראינה].