Shelach

This Torah portion describes Israel’s refusal to enter the land of Canaan after hearing the evil report of the ten spies. How is this considered the worst sin committed by Israel in the Torah? Why is fear called “Satan’s calling card”? How does fear affect the brain? Why is fear actually considered a sin? Is there really such a thing as a fearful believer? How did fear infuse the Israelites with what appeared as courage? And was it genuine courage?