A lot of Quincy objects look crosses, and a number of their attacks reference holy things. For example, there is an attack called "Quincy Vollstandig" which, at least according to the translation I was reading, translated to "Complete Holy Form". Are Quincy as a group Christian (or some other religion) or are these names because they sound cool rather than having any particular meaning?
Religion is an organized collection of beliefs, cultural systems, and world views that relate humanity to the supernatural, and to spirituality.
While it would a stretch to say combating Hollows might be an extension of Quincy culture, it doesn't hold through with a belief system. Religion by definition requires belief, a viewpoint with intangible evidence. When evidence becomes tangible, it holds at least some quantifiable fact.
For Quincy, harnessing spiritual particles to shoot projectiles of energy and the dangers of Hollows interacting with the real world are both instances of fact.
There has been no mention of religion or specifically Christianity in Bleach, but despite either existing, the Quincy are more of a clan of warriors or hunters. I understand the suggestive designs that seem Religion-based but I believe it's to appeal to an exorcist fanbase as a supernatural character option in this story about ghosts, good or bad, and their governors.
No such thing has been specified by the author. Think of it as a cult or clan if you like, but all we know is that their clothes, weapons and name of attacks are due to the their traditions and history (which we don't completely know about just yet).