The transition from the wilderness into the Promised Land requires the Israelites to undergo a profound dual preparation, both practical and spiritual. Standing before the overflowing banks of the Jordan River, the nation faces an impossible crossing. At this critical moment, occurring on the third day of preparations immediately following the thirty-day mourning period for Moses [רש"י], Joshua steps forward to guide them.
He instructs the people to sanctify themselves, a command that the primary approach among commentators understands as a call to readiness. On a practical level, this means gathering their supplies and preparing their belongings for the journey ahead [רש"י, רד"ק, ביאור שטיינזלץ]. Beyond the physical tasks, they must also undergo spiritual purification. Drawing close to divine wonders requires a state of holiness and freedom from impurity [מצודת דוד, ביאור שטיינזלץ]. This spiritual cleansing is particularly necessary because of the nation's fragile state of mind. The Israelites felt unworthy of being led by the Ark of the Covenant, carrying the lingering guilt of their past sin at Peor. By urging them to sanctify themselves, Joshua wants to reassure them that God still values them and considers them worthy of experiencing miracles [אלשיך].
Joshua motivates the nation by promising that on the very next day, the day of the crossing [רש"י, רד"ק], God will perform wonders for them. These wonders will manifest as the splitting of the Jordan River, with its rushing waters standing upright like a solid wall [רד"ק]. Interestingly, Joshua makes this bold promise before God explicitly informs him of the impending miracle. Commentators offer different perspectives on how he knew what would happen. One approach suggests that Joshua simply looked at the natural reality. Knowing they were commanded to cross within three days while the river was overflowing its banks, he deduced that such a feat would be entirely impossible without a supernatural event [רד"ק]. Another viewpoint attributes his foresight to the Ark of the Covenant. Seeing the priests carrying the Ark, Joshua understood that its presence naturally brings about open miracles, just as it had in other historical moments [מלבי"ם].
Joshua assures the people that these wonders will happen directly in their midst, though commentators differ on the exact meaning of this presence. Some explain that Joshua believed the miracles would occur specifically because of the merit and spiritual power of the Israelites, which is exactly why he demanded they sanctify themselves to earn it [מלבי"ם]. Conversely, others suggest that the miracle does not stem from the people's merit, but rather from God's immense mercy. When God performs a miracle out of His mercy, He does so openly and publicly, allowing the nation to witness the divine wonders unfolding right before their eyes [חומת אנך].