The original failure of the spies left a deep scar on the destiny of the Israelites, resulting in a prolonged and tragic delay on their journey to the Promised Land. God's anger over the people's ingratitude meant they were forced to wait in the wilderness until the entire generation that sinned had passed away.
The nature of this waiting period is a subject of discussion. The primary approach among commentators is that this era was defined by constant wandering, instability, and restlessness, imposed as a punishment while the nation waited for the guilty generation to die. On the other hand, a surprising perspective suggests that even within these years of penalty, God continued to grant the Israelites a pleasant life in the wilderness, lovingly supplying them with manna, quail, and water [שפתי כהן]. From a literary standpoint, this restless wandering served as poetic justice; those who had previously shaken and discouraged the hearts of the people were punished with their own physical shaking and wandering [ברכת אשר].
This historical background reveals the depth of Moses' anxiety when the tribes of Gad and Reuben ask to settle outside the Promised Land. The original punishment for the spies was actually composed of two separate decrees: an absolute oath that the older generation would die in the wilderness, and a decree of wandering for the younger generation for forty years [העמק דבר]. Moses realizes that while the decree of death is final, the decree of wandering can easily be extended.
He warns the tribes that just as innocent children in the past were forced to wander and suffer because of their parents' sins, their current actions could bring about another delay for all the Israelites [אלשיך]. Moses emphasizes that the nation has not yet been completely cleansed from the anger of that original sin, which was the climax of ten times the Israelites tested God. In such a fragile state, the cup is already full. Even a relatively small offense, or the adoption of a bad culture and a lack of basic respect, could be the drop that makes it overflow. Moses fears that if these tribes turn away from God, they will reawaken strict justice and unleash a destructive force that does not distinguish between the righteous and the wicked, potentially leaving the entire nation to perish in the wilderness [אלשיך, העמק דבר].