Perfect peace can only be attained by our first receiving God's gift (Jesus) on the cross and then keeping our minds on Him, as Isaiah directed in 26:3: "You will keep him in perfect peace, whose mind is stayed on you, because he trusts you."
True peace, a precious gift from our Heavenly Father, is achieved only when we allow Him to direct our lives: "Trust in the Lord with all your heart; and lean not on your own understanding. In all your ways acknowledge Him and He will direct your paths" (Proverbs 3:5-6)

"You will keep him in perfect peace, whose mind is stayed on you, because he trusts you."