Hebrews 11:6 - "But without faith it is impossible to please Him: for he that cometh to God must believe that He is, and that He is a rewarder of them that diligently seek Him."
All fear is rooted in the notion the God's promises won't come to pass. Fear of poverty is really fear that Philippians 4:19 (concerning God providing all my needs) won't work. Fear of sickness is really the fear that 1 Peter 2:24 (concerning God's promise to heal me) won't work.
I know that God responds to my faith and not my fears.
As I hear God's Word and affirm it and meditate on it, day and night, faith will come.
Likewise, if I listen to and receive satan's word's which put me in doubt and unbelief, fear will be amplified in my life.