Leadership and fear can't dwell in the same tent. Joshua knew on a human level that the odds were stacked against the children of Israel. His faith was not in the circumstances surrounding him. His faith was in the God who parted the Red Sea. If He could lead them through the Red Sea, then certainly He could lead them through the Jordan River.
Leadership demands courage.
When God gets ready to raise up a new generation of leaders, He will always look into the hearts of the people for someone who has courage. Such courage only comes from having been in the presence of God. He knew the presence of God. It was God's presence that prepared Joshua to face the giants in the land. Every generation needs men and women of courage.