What exactly is “the religious life of an atheist?” I think you may need to rephrase your question here, since even the “religious life of a Muslim” necessarily contains explicit statements of belief which conflict with Christianity.
To answer what I think you’re asking, most Christian denominations would accept that essential Christian beliefs can be summed up by the Nicene Creed. (To summarize, it is a statement of belief that Jesus is God, he died for our sins, he was resurrected on the 3rd day, and he will return). That represents the core definition, the minimal requirements for who is or is not a Christian. Required practices vary from denomination to denomination. Christianity is primarily a religion of creed, not practice. It’s defined by what the adherent believes, not what he does. If you perform every Catholic practice, but have no belief in God, you’re not a Christian. If you perform NO denominational practices at all, but accept the creed, you’re a Christian.
Yes. It was called the Council of Nicea in 325 CE.
Some do, some don’t. Some Christians decry all organized churches and rely on the Bible alone. What really makes the Creed “essential” is not that it derives from an authoritative declaration, but that it’s the common denominator. It’s the core that all denominations share and recognize as essential. They might not all recognize it as sufficient, but it’s the part they all recognize as necessary, which cannot be said of any specific practices.
RNATB is a little bit off on Islam. What is essential to Islam is really the Pillars – the 5 specific practices. Most Muslims will say that even if you believe in basic Muslim doctrine (“There is no God but God, and Mohammed was his prophet”), but do not engage in the physical practices of prayer 5 times a day, fasting during Ramadan, etc, that you are still not a Muslim. Unlike Christianity, Islam is a religion of essential practice as well as belief.
This is where you’re wrong. The goal of enlightement, and basic acceptance of the 4 Noble truths is really the only thing that is common to all forms of Buddhism.
You’re making my point for me. This is exactly what we’ve been trying to say to you. Just because, for instance, a lot of Buddhists believe in reincarnation, that does not make reincarnation an essential Buddhist belief.
No, by “no metaphysical beliefs,” I mean, for lack of a better word, no supernatural beliefs.
I don’t think that any metaphysical belief is NOT religious. I think it’s one and the same. Any belief that anything exists outside of, or transcendent of the plain, physical universe is a religious belief.