Joshua's desperate cry expresses a deep, twofold anxiety: an immediate existential threat to the survival of the Israelites, coupled with a severe theological crisis regarding God's reputation in the world. Once the surrounding nations hear that an enemy has successfully chased the Israelites [מצודת דוד], they will realize that this once-feared people can be easily defeated [ביאור שטיינזלץ]. This dangerous discovery will prompt the Canaanite nations to unite into a single front [מלבי״ם]. They will gather a massive army and surround the Israelites with the clear goal of destroying them completely [ביאור שטיינזלץ]. Ultimately, this will wipe out the memory of the Israelites, erasing a name that had previously stood as a worldwide symbol of bravery [מלבי״ם].
Yet, the distress goes far beyond the physical loss of the nation, leading to a profound question about what will happen to God's great name. The primary approach among commentators focuses on the fear that God's name will be disgraced. If the Israelites are wiped out, the nations of the world will naturally conclude that God's power has faded. They will assume the nation perished simply because its God lacked the ability to save them [רש״י, רד״ק, מצודת דוד]. Because God's reputation as a protector and shield became known globally specifically through the bravery and success of the Israelites, erasing the nation will inevitably destroy the great fame God has already established [מלבי״ם].
Other commentators point to a deeper, more essential connection between the people and their Creator. In this view, God's name is directly shared and tightly bound with the name of the Israelites [רש״י, ביאור שטיינזלץ]. Just as a human king might save someone simply because that person carries the royal name, God is certainly expected to save the nation with whom He chose to share His own name, especially since they place all their trust in Him [חומת אנך]. Therefore, the destruction of the Israelites is not merely a national tragedy. It is a direct blow to God Himself, as His very name and presence in the world are forever tied to their fate.