McLuhan's dissertation, "The Classical Trivium," is well worth the read:

https://www.amazon.com/Classical-Trivium-Place-Thomas-Learni...

His faith background plays out more explicitly in his doctoral thesis; several ideas therein were precursors to his later-popularized notions:

https://www.amazon.com/Classical-Trivium-Place-Thomas-Learni...

Short review summarizing the work: https://www.researchgate.net/profile/Phil_Rose/publication/3...