God will keep in perfect peace; peace of heart, peace of mind, peace with others, peace with present circumstances.
Our minds and our hearts are interconnected. Our thoughts affect our emotions, which in turn affect our behaviour, and how we respond to others and the circumstances in our lives.
Setting our minds on Him, thinking on His character and His precepts, will help us make decisions and choices with wisdom and understanding, resulting in peace.
Isa 26:3 Thou wilt keep him in perfect peace, whose mind is stayed on thee: because he trusteth in thee.