The reason believing with your heart is so important, is that when Jesus went down into hell and paralyzed the devil, the devil still had a voice. To me that means that the devil can try to persuade me with ideas or thoughts, but if I believe in my HEART (or spirit) then I'm unshakable and the devil will not be able to deceive me.
A good study is to follow the progression of physical life, accompanied by a God breathed soul life, followed for those in faith alone in Christ alone with a reborn spirit,...our thinking processed through the soul and when processed by the indwelling of the Spirit, helps to sanctify our spirit through the heart. Our outward speaking which may inflence the spirit is from the heart.
A continuing walk in faith offers to fill up to perfection a man of body, soul and spirit. This doesn't deny the physical, rather it fulfills all that has been created.
We might witness the physical decay of bodies we percieve and reason to associate with the vessals of life, but ressurection is large eye-opener. Not only does one have newness of life in the spirit upon regeneration, but in time we will also be given a resurrected body.
Until science can grasp these issues it is merely a cheap panacea for reality.