How to define "Religion" as a whole?

^ I think the purpose thing applies to more modern religion.

Personally I agree with Shidoshi's definition. Religion at its essence was something to provide an explanation to the unknown. Humans fear the uncontrollable/unknown, so religion not only gave them a "comprehensible" explanation, but also a sense of comfort.

Nowadays, the most popular ones focuses more on giving an individual a purpose for their life, and it proposes a certain lifestyle instead of providing answers(science has pretty much taken that role). Imo, this definition does not apply to religion as a whole though. It's pretty hard to give a short description of what religion if one focuses on it as a whole and what it meant for people back in the past and in the present.

Interesting topic.

I think it still applies to religions even younger, especially since they were in such fathom, corruption and lack of comfort in general. It was kind of "If I'm a good person, I'll be rewarded with infinitive leisure!"(This is just a general, thought process, I'm aware it's a lot more complicated). It was by blood, not work that made you successful or not. Though I do see how modern religion priorities have changed since, as you say, science is quickly overlapping it.