Unfortunately, it seems that skeptics sometimes choose to take it on faith that this is the proper way to understand faith. In point of fact, “faith” as it is used in the New Testament (pistis) simply refers to “trust.” In general, of course, trust can either be well-placed or ill-placed, depending on the object in which one is trusting. As such, it need not preclude the offering of evidence and argument, though it can in certain instances. If one accepts the claim that God exists by faith, for example, one does not believe it on the basis of a demonstration obtained through one’s own discursive efforts. Though this could mean that the belief is formed in the absence of evidence, it could also mean that the evidence merely consists of a certain kind of immediate experience—just as is the case with respect to belief in the external world, or even in one’s own existence.
In other instances, one can accept a claim by faith through trusting a particular authority’s claim to have made the proper demonstration. For example, in accepting medical diagnoses one trusts that the judgment of the physician is based on their having made an adequate demonstration to the effect that a particular illness is giving rise to certain effects.
Fundamentally, then, the essence of faith is the acceptance of a particular claim as true, the demonstration of which is not presently accessible to the cognitive agent in question. The rationality of one’s faith (or lack thereof) will then turn on whether a demonstration of the relevant sort is accessible to someone. If yes, then one’s faith is reasonable. Otherwise, it is not.