Do you mean:
* The Dark Tower series by Stephen King? This series features a quest narrative, the struggle between good and evil, and themes of friendship, sacrifice, and the nature of reality.
* The Roland of Gard series by Rosemary Sutcliff? This historical fiction series focuses on the life of a young knight in medieval England.
* Other books featuring a character named Roland?
Once you clarify which books you're referring to, I can provide a more specific answer about their themes.