This is a Buddhist belief structure in where the inescapable law of kamma guarantees that each and every one of our actions — whether it be of body, speech, or mind — has consequences in line with the skillfulness or unskillfulness of that action. We can often witness this process first-hand in our own lives, even if the effects may not be immediately apparent. But the Buddha also taught that our actions have effects that extend far beyond our present life, determining the quality of rebirth we can expect after death: act in wholesome, skillful ways and you are destined for a favourable rebirth; act in unwholesome, unskillful ways and an unpleasant rebirth awaits. Thus we coast for aeons through samsara, propelled from one birth to the next by the quality of our choices and our actions.

The suttas describe thirty-one distinct "planes" or "realms" of existence into which beings can be reborn during this long wandering through samsara. These range from the extraordinarily dark, grim, and painful hell realms all the way up to the most sublime, refined, and exquisitely blissful heaven realms. Existence in every realm is impermanent; in Buddhist cosmology there is no eternal heaven or hell. Beings are born into a particular realm according to both their past kamma and their kamma at the moment of death. When the kammic force that propelled them to that realm is finally exhausted, they pass away, taking rebirth once again elsewhere according to their kamma. And so the wearisome cycle continues.

The realms of existence are customarily divided into three distinct "worlds" (loka), listed here in descending order of refinement:

* The Immaterial World (arupa-loka). Consists of four realms that are accessible to those who pass away while meditating in the formless jhanas.
* The Fine-Material World (rupa-loka). Consists of sixteen realms whose inhabitants (the devas) experience extremely refined degrees of mental pleasure. These realms are accessible to those who have attained at least some level of jhana and who have thereby managed to (temporarily) suppress hatred and ill-will. They are said to possess extremely refined bodies of pure light. The highest of these realms, the Pure Abodes, are accessible only to those who have attained to "non-returning," the third stage of Awakening. The Fine-Material World and the Immaterial World together constitute the "heavens" (sagga).
* The Sensuous World (kama-loka). Consists of eleven realms in which experience — both pleasurable and not — is dominated by the five senses. Seven of these realms are favourable destinations, and include our own human realm as well as several realms occupied by devas. The lowest realms are the four "bad" destinations, which include the animal and hell realms.

It is pointless to debate whether these realms are real or simply fanciful metaphors that describe the various mind-states we might experience in this lifetime. The real message of this cosmology is this: unless we take steps to break free of the iron grip of kamma, we are doomed to wander aimlessly from one state to another, with true peace and satisfaction forever out of reach. The Buddha's revolutionary discovery came in finding that there is a way to break free: the Noble Eightfold Path, which equips us with precisely the tools we need to escape from this wearisome wandering, once and for all, to a true and unshakable freedom.