Hola Christi

Eso has the same function as aquello when talking about an idea. We mention the same thing about "eso" in the lesson about ese, esa, esos, esas and eso. Have a look here.

I would say the difference between eso and aquello is that "aquello" is used when in our mind the idea we are referring to feels as something far away in time or space, while "eso" feels closer to us somehow. 

It is a very abstract idea so using one or the other will depend on how each individual feels about something.

I hope this helps

Inma