The Six Realms of Existence
For Buddhists, these six realms represent all possible states of existence. They were traditionally conceived as real places, but can also be interpreted symbolically. The animal, ghost and hell realms are all places of punishment for previous sins, whereas birth in the heavenly, asura, or human realms comes through the accumulation (and spending) of karmic merit. Life in any of these realms is ultimately impermanent—one does not suffer forever in hell, nor enjoy eternal bliss in heaven.
Birth in any of these realms is based on one's karma (“action”)—essentially the moral causality that good actions bring good results, and bad actions bad results. Since one’s motive is critical for “goodness” or “badness,” one’s thoughts become at least as important as one’s actions (for example, accidentally killing something is far less serious than intentional killing).
Karma presupposes a dynamic universe--one's present life reflects past choices, but one's present choices are shaping the future. Only human beings can make choices and accrue karma, which means that one's human actions (good or bad) determine one's future births. This gives added emphasis to one’s moral choices; it also means that a change of heart or better guidance can help one to lay a positive foundation for the future. Such guidance can range from simple moral precepts (as found in board games such as Snakes and Ladders) all the way to instructions on how to select one’s next birth, as found in the final section of The Tibetan Book of the Dead.
Note that each of these realms has a resident Buddha, through which its inhabitants can hear the dharma—this may reflect the Mahayana Buddhist notion that the ultimate Buddha-nature (dharmakaya or Suchness) pervades the entire universe. The six realms are: