To improve anything you need to know how it works (brains, bodies, fields of study, concepts, etc)
Usually, "improvement" simply and practically means: "To make it your own"
I'm only 60% sure, but I think the "higher universe" of angels, etc, feels to mortals like "extreme freedom" and our brains can't comprehend it
I think that technically we can survive there, but need a very long time to fully adjust (more than a few years), and that's only after we're fully prepare to enter it (which must also take a few years to prepare for)