I just finished applying to graduate programs in clinical psychology, so I'm not an expert on what graduate schools look for in Religious Studies applicants, but I also had to discuss my research interests in my SOP so I will try to help. It is okay to write broad topics as your research interests; graduate schools understand that, as an incoming student, you're not going to be 100% certain on what narrow/specific thing to study. It is more important that your general research interests fit well with those of the faculty in that program. When I wrote my SOPs, I took a little time to briefly read an article or two written by the current faculty. In my SOP, I mentioned something specific from their research article that I found interesting. I don't think that you need to quote their work, but I think that it's a good idea to discuss what specifically interests you about the publication and why you would be a good fit to work with that person based on their current research. As far as writing about your research interests, just briefly write about your broad interests and areas that you would like to get into.