There are quite a lot of varying degrees of casual believers in religion. I grew up in a family of Christians/Catholics who never go to church, rarely say grace, have never personally read the Bible, but still believe in God/afterlife/etc and have personal beliefs that are molded from religious teachings.
I know at least for the Christian based religious groups I'm aware of, you don't even need to share faith to be part of the community.
Believe it or not, they don't get into fist fights when they meet someone of another faith either.