A Christian is someone who believes in the Christian religion. Same with a Muslim, Hindu, etc. Being a Jew is a lot more complicated. It's an ethnicity and a religion. I like to compare it to being an Irish Catholic. You can be a Jew the way someone is Catholic. But you can also be a Jew the way someone is Irish. That's why someone who is not born Jewish has to go through conversion to be considered Jewish--to be counted in a minyan and so forth. But if you're born Jewish, with a Jewish mother, you're Jewish, no matter what you believe or how you behave. Consider me. My parents were both atheists. My father was raised atheist. We observed no holidays and only went to synagogue for someone else's wedding or bar mitzvah. But there was never any doubt that we were Jewish. The most Orthodox Jew in the world would have counted me, my father, and my brothers as Jews. My first wife was born and raised Methodist. At a very young age, she married a Jew (not me), and eventually went through a Reform conversion. Years later, that marriage over, she and I visited a Conservative rabbi about getting married. The rabbi had two problems. First, he didn't recognize the Reform conversion. She'd have to undergo a Conservative or Orthodox one. She was willing to do so. The second problem at first seemed more difficult. She and her first husband only had a secular, state divorce. The rabbi didn't recognize that. She needed a get (Jewish divorce). In those days, a Conservative get required the husband's permission, and she wasn't on talking terms with her ex. Within a few minutes, the rabbi came up with a solution. Since he didn't yet consider her a Jew, he didn't consider them married. Problem dissolved. She went through the conversion and we got married. btw, when we got divorced, we mutually agreed to get a get, which we did through a Reconstructionist rabbi. It was a beautiful and healing experience, that involved us apologizing to each other in front of witnesses.