Hebrews 10:39

But our way is not that of those who shrink back to destruction, but (we are) those who believe (relying on God through faith in Jesus Christ, the Messiah) and by this confidence faith preserve the soul. 

All fear opposes faith and wears away our confidence in God and His word.  Fear is what causes us to shrink back to destruction and weakens our confidence. When faith dominates the heart and mind fear is not tolerated and the thoughts not allowed in. Faith teaches us to be brave because we know that God is at work in our lives.