It's interesting how different stories have different underlying religious underpinnings in different parts of the world. It's important to consider that these themes are precisely because the stories are born from the surrounding culture.

Christian references in the Cantos were probably incidental, given the expected familiarity of the intended audience (american white male young men). eg The Matrix trilogy started with the obvious messianic hero's journey, then attempted to expand it in the following films (karma, cycles of death and rebirth, etc).

For some, these religious messages can be a turn off, I agree. I happened to be raised in a culture that allowed me to ignore it more or less and I can recognize that.

Not sure if I agree with the christian references being incidental ... the first book is literally a retelling of the The Canterbury Tales, all the characters are on a pilgrimage. there are a bunch of religious groups with at least one being central to the story, there are cross shaped parasites that grant eternal life.

I still think you can enjoy it without caring much about religion.

>Christian references in the Cantos were probably incidental,

They're not at all incidental. The themes and the literal Catholic Church don't just make it into the books by osmosis, they're central to it and deliberate.

Like Gene Wolfe he's part of a pretty small group of US authors who wrote Catholic speculative fiction. Like Wolfe his writing is also fairly un-American. If Heinlein or Asimov are examples of archetypal US science fiction, Simmons is about as far as the other end as you can be, with the post-modern structure, the Canterbury Tales as a template for the story and so on.