Judaism: A State Of Mind
The best definition I ever heard of the whole problem was from the late Pastor Robert Miles:
"Jews aren't a race, and Judaism is not a religion. Judaism is a state of mind, and some of the worst Jews you will ever meet won't have a drop of Hebrew blood in their veins."
I now understand exactly what Bob meant. Judaism is essentially the rejection of Man as a spiritual being and the reduction of life to pourely material terms: both Communism and capitalism are, in fact, forms of Judaism.