Those who know God fear God.

 The Lord is my light and my salvation; whom shall I fear? The Lord is the stronghold of my life; of whom shall I be afraid?

Psalm 27:1 (ESV)
 
Fear drives us. We fear people, failure, death, life, and more, and whatever we fear controls us.
It should be evident that God loves us and that no force, no matter its apparent strength, can stand against Him. Our fear of God gives us the ability to trust in God, and our trust in God gives us the peace that passes all understanding, regardless of our situations in life.
 
The fear of many circumstances has never yielded peace; it only causes stress, anxiety, and hopelessness. The fear of God is the beginning of wisdom. Trusting in God is the ultimate goal, and that goal is a byproduct.
 
Those who know God fear God, and the final verse of Psalm 27 is the byproduct. They are those who can wait on the Lord, for they know He will come through. They can be strong, for they trust in His strength. Their heart is courageously hopeful.