Isaiah 26:4 

Trust (confidently) in the Lord forever (He is your fortress, your shield, your banner), for the Lord God is an everlasting Rock (the Rock of Ages).

God is the beginning and the end, possessing incomprehensible power which He uses for His people. When we trust in Him, doubts and worries leave our minds; we let God work instead of trying to fix everything ourselves. Trust confidently in the Lord and His promises.