The 'Screwtape Letters' by C.S. Lewis is a great choice for teens. It offers a unique perspective as it's written as a series of letters from a senior demon to his nephew, guiding him on how to tempt a human. It's a thought - provoking read that can help teens understand the nature of spiritual warfare and the importance of their faith.
'The Door Within' trilogy by Wayne Thomas Batson is an exciting series for teens. It's filled with knights, battles, and quests, but also has strong Christian values woven throughout. The main character discovers a door within his own heart that leads to a world where he must fight for what is right and good, in the name of the King, which is a metaphor for God.