rockpie, religious faith plainly is not rational. A fallacy commonly employed by religionists is assigning the quality of their concept of "faith" - which of necessity and by definition is falsely
a priori, inherently and functionally irrespective of observed fact, inconsistent with
Occam's Razor, wholly
inductive, a self-defeating
modus ponens/modus tollens argument invalid (see:
Formal Validity) in that it perforce must proceed from the illicit, undemonstrated premise that there be a god or gods - to any empirically founded, rational,
a posteriori, evidence-based worldview.
It is not "faith" which compells a planet to hold its orbit, for instance, it is physics, and no "leap of faith" is entailed in both inductively and deductively arriving at the discovery and understanding of the laws and principles of physics; the math works to confirm the relationships among the observed phenomena.
Before you even may begin to address the question of Christianity's validity, or the validity of any religion, for that matter, first you must demonstrate, objectively and in academically sound, forensically valid manner, that religious faith be differentiable from superstition.