Supernatural Religion
The line between Good and Evil in supernatural is initally very clear as Sam and Dean winchester are seen to be on the good side of the line and the supernatural world on the other side. However as the show progressed the line between good and evil becomes blurred, which means that not everything is as it appeares to be or what it is traditionally interpreted as. Christainitiy would traditionally view good and evil through god in heaven and the devil in hell, however supernatural takes this idea and flips it around. Supernatural explores good evil in the early seasons through the various supernatural creatures that the brothers hunt down every week. In the more recent seasons the show has started to focus more on the conflict between the angels and the demons through each group, but also through individual Characters. The show addresses the theme of good and evil in other religons in certain episodes such as "Hammer of the Gods" from season 5.
Ghosts and monsters played a big part in the shows early seasons when there would be a monster of the week. Traditonally spirits and monsters are mostly considerd to be evil but on supernatural they may turn out to be so evil after all. The show much of the time will intially represent many of these creatures as good or evil, it will then delve into their motives and nature making you second what they are. Their motives and nature also make the brothers and the audience question if they are really repsonsible for thier actions and if that makes them good, evil or a bit of both.
Angels and Demons became a central part of Supernatural right at the start of season 4 with the two sides waging a war with each other. Although it can be seen that the war was sometimes mostly just within the Angels themselves then with the demons, but the two groups do despise one another. Angels are typically seen by society as being completly good protecting humanity and serving god. But on Supernatural the angels are far from being these the good guys as many of the angles are actually quite evil. The Demons who in a christain society are typically viewed as evil are most;y represetned as such. Supernatural protrays the Demons as being cruel and sadistic often taking pleasure in the pain of humans.