I remember in 7th grade, my parents had the bright idea to send me to a private Christian school, since I wasn't doing well in public. It was not a good fit, and I got sent to he library as a punishment regularly. This was a pretty terrible library for a 7th grader, since it was all preachy stuff. The one decent author I found was Stephen R. Lawhead. He had a scifi series about living on Mars and I enjoyed it. Then I read some fantasy books he wrote. I'd say that led me to a lot of the older fantasy and scifi stuff I eventually read. I don't really remember it being heavy on the Christian themes, at least not any more than CS Lewis. So that helped.