Supernatural has a unique way of accounting for the simultaneous existence of an all-powerful God and the various Old Gods taken from ancient mythology. The world of Supernatural is no place for an atheist, with each passing season seemingly confirming more and more of humanity's various religious figures to be the real deal. As well as introducing the concepts of Heaven and Hell, Supernatural has revealed an all-powerful creator in the form of Chuck Shurley - a being responsible for the existence of all life. However, Chuck is far from the only religious deity to appear in Supernatural, with the show drawing inspiration from a wide selection of faiths and mythologies, and this creates a potential paradox.
Philosophers and non-believers have long propagated the idea that mankind has worshiped so many different Gods and followed so many varying religious faiths that all of them can't possibly be true - with the intricacies of one belief system making it incompatible alongside the others. Fortunately, Supernatural makes no attempt to solve a problem that has baffled the greatest minds in human history, but it does account for how Chuck Shurley can be considered the one true God of Supernatural, while also including an array of other religious idols.
Supernatural is intentionally flexible about which religion the likes of Chuck, Lucifer and Castiel are supposed to represent. On a surface level, the series draws heavily from Christianity - particularly with regards to names, appearances and hierarchy - and this is likely because Supernatural is produced and set within a predominantly Christian locale. However, aspects of other faiths are incorporated into the mythos, such as the scene in season 14 where the archangel Michael visits a Muslim man and quotes from the Qur'an. Despite the Christian overtones, it's clear that Chuck is intended to represent all of the primary modern monotheistic belief systems. The details and methods of worship may differ between religions but as far as the world of Supernatural is concerned, anyone praying to a single, omnipotent God is praying to Chuck.
This doesn't, however, address the existence of the Old Gods in Supernatural. Since its very first season, Supernatural has incorporated deities from a wide range of ancient mythologies, borrowing repeatedly from Pagan, Greek, Roman and Norse lore. While these beings are referred to by the same lofty title as Chuck, they function very differently in Supernatural, as where Chuck's power appears to be entirely his own, the strength of the Old Gods is directly proportionate to the amount of followers they have. This explains why the likes of Anubis and Zeus were revered as immortals thousands of years ago, but can be killed with relative ease in the 2000s.
Arguably, this balance is achieved by demoting figures that real-world human history dictates should be on-par with Chuck to little more than a particularly formidable species of mortals, meaning the likes of Odin, who could've potentially been a major recurring character, are relegated to a single appearance. The trade-off is Chuck's establishment as Supernatural's overall supreme deity, giving Sam and Dean someone to turn to when things get really hairy, and providing an undisputed final villain for Supernatural season 15.
Predictably, Supernatural's presentation of religion is not without flaws. Although many of the Old Gods are no longer actively worshiped in the modern civilization, allowing their image to be used largely without fear of causing offense, some major religious figures have been, perhaps wrongly, lumped into this category. In Supernatural season 5's "Hammer of the Gods," much of the show's Old God lore is established, but in addition to the Norse and Roman names introduced, the episode also features figures from Hinduism. The roots of Hinduism are undoubtedly ancient, but the religion remains one of the most practiced faiths in the world and many followers were unhappy with how Kali in particular was portrayed.
For a series about saving people and hunting things, the tricky waters of religion are tough to navigate and although Supernatural's theology may not be perfect, it has allowed for many different belief systems to coexist within one fictional world.
Supernatural season 15 premieres October 10th on The CW.