After death the transmigrating soul you are greeted by other beings. Swami Nishreyaan Ji who started our Vedanta work in South Africa he had these nice stories to explain these concepts of temporary worlds you visit. When your karma is exhausted you sent back here or the hells when suffering is over you come back again. Now among all of them there is one highest heaven highest in the sense the best one which is a very spiritual world.
Swami Sarvapriyananda teaches one of the shortest and most profound upanishads accompanied by Gaudapada's Karika. This lecture covers Karika 22-23 and Mantra 12.