Certainly it is true that there is a point in the exercise of faith at which we must act simply. A point at which we must simply decide to be a believer or not. But faith itself is most certainly not simple in the sense of being obvious or uncomplicated. Faith is as complicated, as complex as is human nature itself. Those who truly believe, bring into that act of faith every ability, every power, every sensitivity at their disposal.
Faith involves the intelligence, the emotions, the instincts, the appetites.
And I suppose most directly of all, it involves the one ability that sort of draws all the rest together, the ability to judge, to make a decision, to order oneself, and give direction to one's life. And perhaps that is as good a way as any to define faith. The process of giving order and purpose, meaning and value to every aspect of our lives. And doing so by following as closely as possible the example set down for us by Christ Himself. So before it is anything else, faith is a kind of letting go of oneself, a self-surrender, and an acceptance of the person of Christ as the major force in one's own life.