Heaven—at some point in time, all cultivators dream of becoming immortals and ascending to Heaven. But Heaven isn't a place, rather it is the entity in which the Celestial Paradise dwells. And while that Celestial Paradise doesn't discriminate between mortal and upper realm immortals, the factions that compose it don't see kindly to the ascension of mortals—often seen as riddled with the polluted bodies and cultures of the "lower" realm.
Lots of info in this chap. But I felt that it was time you guys got some knowledge of the pantheons we've been talking about all along and the inner workings of Heaven. Don't feel the need to remember everything, I will feed you all that you need to know.