Commentaries:
Notice the spies' timidity even at the beginning of their report, and they become increasingly fearful. If, because of God's promises in Exodus 23, they did not expect confrontation, why do they show so much trepidation? Even Joshua and Caleb expected confrontation. They most certainly did not understand that God's promises in Exodus 23 would be fulfilled without them having to lift so much as a finger to gain the land. They knew they would have to make war against the people of the land.
The underlying problem was that they did not trust that the warfare would be a cooperative effort. In effect, they believed that God could not do it. They did not trust that God would be with them, cooperating with them and fighting on their side against the common enemy, the people of the land. Joshua and Caleb knew there would be combat, but the difference was that they were confident that God would fight for Israel and against the Canaanites.
John W. Ritenbaugh
The Christian Fight (Part One)