Perfect Peace is Based on Perfect Trust

"3Thou wilt keep him in perfect peace, whose mind is stayed on thee: because he trusteth in thee. "

This verse could just as well be translated

The mind at rest is kept in perfect peace because he trusts

Then the next verse gives more clarity:

"4Trust ye in the LORD for ever: for in the LORD JEHOVAH is everlasting strength:"

So

The mind at rest is kept in perfect peace because he trusts full in the Lord.

Because you trust in Him, you believe that He is your strength:

"The LORD is my strength and my shield; my heart trusted in him, and I am helped: therefore my heart greatly rejoiceth; and with my song will I praise him." (Psalm 28: 7)

and

"I can do all things through Christ which strengtheneth me." (Philippians 4: 13)

We see Christ Jesus as our full provision:

" 31What shall we then say to these things? If God be for us, who can be against us? 32He that spared not his own Son, but delivered him up for us all, how shall he not with him also freely give us all things? (Romans 8: 31-32)

and

"But my God shall supply all your need according to his riches in glory by Christ Jesus." (Philippians 4: 19)

When we trust in the Lord, we are able to do good, to dwell in the land, and live off His faithfulness:

"Trust in the LORD, and do good; so shalt thou dwell in the land, and verily thou shalt be fed." (Psalm 37: 3)

and

"The LORD is my strength and my shield; my heart trusted in him, and I am helped: therefore my heart greatly rejoiceth; and with my song will I praise him." (Psalm 28: 7)

Perfect Peace is based on Perfect Trust, and we can have this perfect truth in Him because He has perfected us by His death on the Cross (Hebrews 10: 14)