At some point in time, humans became religious. (One might argue that it's at that point that our ancestors became truly human.) Maybe before that they were concerned only with practical, physical things like eating and mating and surviving. But something happened. They started to have spiritual ideas. There are archaeological sites in which human beings were buried with grave goods - probably indicating a belief in an afterlife - dating back 100,000 years. Too, they carved figures of imaginary creatures -- part human, part animal.
These developments in human society are seen - by archaeologists and anthropologists - as advances. The human mind had developed to the point where it could have more spiritual awareness.
Contrast that with today. Now, a belief in spiritual realities is viewed by many people as a backward thing; something that should be sloughed off by practical, physical, scientific minds.
So, what was it - a passing phase that we can now dispense with? Or a genuine, watershed advance that was the key part of being human?
(And ask yourself... what would Screwtape want you to think?)