The promise of a homeland to the Israelites is not a passive gift simply handed over to them. Instead, it demands an active partnership that blends divine assurance with human effort. God grants the people the strength and ability to inherit the land, but turning that promise into reality depends entirely on their willingness to step forward and take action.
The guarantee of the land is established as a reality that has already been given, indicating that the territory has belonged to them since the days of Moses, when God assured that the next generation would enter [אלשיך]. The primary approach among commentators is that God promises to provide the necessary power for conquest [רד״ק]. However, this comes with a strict warning. The Israelites must move quickly and purposefully to capture the land; they cannot simply hide and expect God to fight the battles for them [אברבנאל]. Others emphasize a slightly different balance, noting that while human effort is required, the actual conquest is fundamentally carried out by God. The physical act of marching is merely the people doing their required part [אלשיך].
On a deeper level, the nature of this conquest could have been entirely different. If the Israelites had been perfect in their behavior, the mere act of stepping foot on the ground would have caused their enemies to collapse without any need for weapons or warfare, exactly as it was meant to be during the time of Moses. It was only due to the people's past sins that natural warfare became necessary. Consequently, the divine promise became conditional, requiring them to first conquer the land through conventional means and improve their actions [מלבי״ם].
The scope of this territorial promise is vast, extending even beyond the official borders of the Land of Israel. If the people choose to conquer territories outside these boundaries, those areas will belong to them and will be infused with the same holiness as the Land of Israel itself [רש״י, רד״ק, ביאור שטיינזלץ, אברבנאל]. However, expanding outward is entirely optional and is only permitted after the conquest of the primary land is completely finished [רש״י, מלבי״ם]. Because the realization of this promise is tied directly to where the people actually march, God knew beforehand that they would not conquer the entire promised territory right away. As a result, the complete fulfillment of securing all the promised borders was delayed, only coming to full fruition generations later during the reign of King David [אלשיך].