Christian author, Lynne Collier, writes Christian Speculative Fiction and Fantasy. Here she explains the differences between overt and non-overt fiction.
What Is Christian Speculative Fiction?

“Biblical [Christian] Speculative Fiction is speculative fiction which uses Christian themes and incorporates the Christian worldview…” — Wikipedia.
In many of the modern Christian fiction novels, the characters are mainly Christian and act on guidance from God with no overt or miraculous divine intervention. There is almost always a non-Christian character who eventually becomes ‘born again’ and the emphasis is biblical and doctrinal, as in Tim LaHaye and Jerry B. Jenkins’ Left Behind series. It differs greatly from speculations on the Bible and Christianity found in fictional work such as Dan Brown’s The Da Vinci Code.
An example of a story which portrays a biblical and doctrinal emphasis but also features miraculous intervention would be Frank Peretti’s This Present Darkness which features demons, angels, and spiritual warfare.
Examples of stories which reflect a Christian worldview without explicitly Christian references would be The Lord of the Rings by RR Tolkien, C.S. Lewis’ The Chronicles of Narnia, and G. K. Chesterton’s The Ball and the Cross, which are overtly miraculous in content…”
Read Lynne Collier’s full blog post at lynnecollier.com