We should want a “sound” (tranquil NASB) (4832) “heart” (3820). And I am assuming that such a thing is within reach of everyone. This could be a statement about stress and blood pressure.
This is really one of the great promises of life in Christ. The word for “tranquil” is most frequently translated “healing” and has the idea of health and cures. When we truly trust in Christ, not only for our salvation, but for our daily care it makes a difference in how we face the day. Jesus promised this inner peace.
(John 14:27 KJV) 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.Since we are also promised persecution if we are faithful, this cannot mean that everything will go smoothly around us. It is an inner promise of peace of “heart” (3820), or mind.
For the outward trials we face we have another promise.
(1 John 4:4 KJV) Ye are of God, little children, and have overcome them: because greater is he that is in you, than he that is in the world.So? We can have inner peace if we trust. We can have outward victory if we have inner peace.