A peaceful mind is part of God's plan for you. God's provision is peace.

Isa 26:3

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

Joh 14:27

Peace I leave with you, my peace I give unto you: not as the world giveth, give I unto you. Let not your heart be troubled, neither let it be afraid.

Col 3:15

 And let the peace of God rule in your hearts, to the which also ye are called in one body; and be ye thankful.