This novel was bought in a Christian bookstore in the 90s. A paperback, in American English. Cover was light colors, mostly white. I think there was a spaceship on the cover. Found in my parents basement on a visit as a "new book" to me at the time - I had voraciously read everything they had before 1990. My mom always bought from the same bookstore, now closed.
In the novel there was an evil galactic empire, with a small plucky group of people who (mostly passively) resisted its rule. These stand-ins for persecuted Christians wore blue stones as jewelry around their necks. When they were in close proximity to another stone (and therefore another believer), both stones would glow. Later these believers found a planet to hide on with lots of these stones. They discovered that the stones could be used as spaceship fuel, better or at least faster than that used by the evil empire, enabling them to escape when they were eventually discovered.
The final confrontation was against a Darth-Vader-like big bad that fought with a glowing red rod against the blue-stone-powered weapon of the main character. The big bad lost when he accidentally hit the dark altar that was the source of his demonic power, causing said power to turn on him.
I saw it as a star wars ripoff at the time for 3 main reasons. 1. It was an implied sprawling space empire with no reference to earth or to any real-world country or nationality. 2. Overwhelmingly powerful evil empire versus small good group of rebels. 3. The lightsaber-like fight at the end. Hopeful glowing blue against darkly throbbing red.
I suspect it was the author's only novel, and published under a generally Christian book imprint like Zondervan or Revell.