Too often the Christian life is approached on the basis of the way things seem to work in the natural order. This is not entirely incorrect in that we do in fact live in this world and are subject the laws and maxims of the natural order...at least as far as the perishable aspects of our lives are concerned.
Therefore, if you jump off a high enough building, you will die. No matter how much you believe that you will not get hurt-no matter how much 'faith' you muster up thinking that you will rise above it all...you will die. Because, having faith, walking by faith, and believing, is not about overthrowing the physical order of things. It is not the primary faculty by which we interface with the natural order.
This is not to say that faith does not inform the way we interface with the natural order, nor that it will not actually affect our behavior in relation to the natural order. It is simply a statement that faith is about, and engages us in, the unseen, spiritual realities of life. It concerns our souls much more directly than it does our bodies (although our bodies will often manifest the results of our faith).
This is why "faith healings" and the whole "Faith Movement" is so wrong. It takes the instrument of faith-which God grants for believing upon Jesus Christ for the salvation of our souls-and makes it primarily an instruments for gaining success or longevity for our bodies. This is not only a miss use of a precious gift, it is the denial and downplaying of a glorious future hope...that hope being the resurrection and transformation of our bodies.
Walking by faith is essentially living (in this life and in our bodies now) in light of the realities of our new identity in Jesus Christ and the blessing promised to us "in Him". That against what we might see around us-that the wicked prosper, people live and then die...never to live again, that to gain you must trample over others, etc.-there is another order, another "kingdom" that this present age will give way to. It is living like we are part of that order-because in Christ we are-and thus living "against nature" in the present evil age.
Faith then is our ability-God given-to reach up into the unseen realm and grasp hold of the realities of the coming age. It is the instrument by which we lay hold of Christ-our Savior, Lord, and life. It is that grace which enables us to live "against nature", but while within it. Not "against" it in the sense of hovering instead of walking, claiming instead of working, believing instead of going to a doctor. But "against" it in the sense of-because of our union with Jesus Christ-we have died to sin and no longer can live in it, valuing now God's glory instead of our own well-being, and seeing death as the doorway into closer union with Jesus Christ because once we die, we will then receive the outcome of our faith...the redemption of our bodies.