Though experiment: say that of the two billion Christians in the world (rounding for simplicity’s sake), 25 percent actually adhere to the dietary,* behavior, and other restrictions of the religion; go to church every Sunday; and genuinely believe in the religion’s dogma. The other 75 percent are just culturally Christian. Now say that of the 1.5 billion Muslims in the world (again, rounding for simplicity’s sake), 35 percent actually adhere to dietary and other restrictions, attend mosque, believe dogma, while the other 65 percent are simply culturally Muslim.
First, do you think that all religions have essentially the same ratio of believers to not-really-believers? If not, which ones do you think have more believers, which do you think have fewer.
If I had to hazard some guesses, I’d say that Judaism likely has the lowest number of people who actually adhere to the religion’s restrictions, observe the holidays, and believe in the dogma. This is based solely on the fact that of the handful of Jews I’ve known in my life, not a one of them was at all a believer in any sense of the word.
On the other hand, I would say that either Islam or some more obscure religion (such as Jainism) has the highest ratio of true believers to half-assed “believers.” Jainism is quite a commitment; you’re not going to claim Jainism unless you’re really into it.
ETA: I know that, by-and-large, Christianity doesn’t have dietary restrictions outside of a few obscure sects. But other religions do, of course.