Yeah I should have said "solely a matter of faith."

Many early scientists and alchemists were driven by a desire to discover through theory and experiment the mind of god. Archeology as a field was largely formalized by members of christian societies hoping to find the historical sites of miraculous events, to bolster their faith. Even as these searches strike out in the 17th, 18th, and early 19th centuries, religion still clung to the near universal belief in material of life being different from inanimate matter. The proof in the existence of god was as simple as looking in a mirror--you were made in his image, and so obviously different from the mechanical substances that made up the rest of the world.

The discovery of evolution as a mechanism for the explanation of life, and the later elaboration of life's mechanical nature really closed off the final possibility of there being everyday real-world proof for the existence of god. It was then that the philosophy was adopted that ALL of religion was a matter of faith alone, untestable by science.

Faith does seem to be a Judeo-Christian-Moslem thing though, rather than something inherent in religion. As far as I can tell, the Indo-European pagan religions were more about practicing the correct rituals, rather than believing the correct things.