Thou wilt keep him in perfect peace, whose mind is stayed on thee: because he trusteth in thee. Isaiah 26:3 KJV
Perfect peace is only found in trusting God.
For the which cause I also suffer these things: nevertheless I am not ashamed: for I know whom I have believed, and am persuaded that he is able to keep that which I have committed unto him against that day. 2 Timothy 1:12 KJV
Wherefore he is able also to save them to the uttermost that come unto God by him, seeing he ever liveth to make intercession for them. Hebrews 7:25 KJV