M
Mystophilus
Guest
Fire cleanses, in that it separates elements from one another. That makes it a useful symbol for purgation.The only sensible answer I can think of is that it is to control people through fear. This is why many today reject the idea.
Also, I like the idea of Purgatory. Without it, there is a zero-width line between the eternally saved and the eternally damned, which seems rather unfair to whoever happens to be the most minimally damned.