The higher planetary systems in this material world are Bhūrloka, Bhuvarloka, Svargaloka, Maharloka, Janaloka, Tapoloka, and up to Satyaloka, or Brahmaloka. Whichever of these planets one rises to in his next life, one must finally return to earth. What to speak of the next life, even in this life the high position one attains after considerable hard work—such as king, emperor, minister, governor, or president—is lost after some time, and one is thrown back to a mean and humble status. Only leaders who have experienced this kind of humiliation can know the trepidation that accompanies it. But if at any stage of life the grossly foolish miscreants described in the Gītā decide to render devotional service to Lord Kṛṣṇa, they can escape the ferris wheel of karma. On this wheel, sometimes one goes to heaven and sometimes to hell, sometimes one is born a king and sometimes a slave, sometimes one becomes a brāhmaṇa and sometimes śūdra, and so it goes on. But once a person enters the spiritual abode of the Supreme Lord, he begins his eternal life in his original, constitutional position.
By the influence of karma, one who is attached to the material body and mind has to change bodies life after life. In this way the soul roams the fourteen planetary systems within this material universe, sometimes going up and sometimes coming down. These planets are transitory—merely theatrical stages upon which the soul enacts his mundane existence. But when the living entity is elevated to spiritual perfection and is situated in his pure, eternal identity, devoid of all mundane designations, he attains the natural habitat of the spirit soul, the supramundane realm transcending this material creation and the intermediary zone of the unmanifested Brahman effulgence.
The material body, made up of material ingredients such as earth, water, fire, and air, is mortal. Similarly, because this material universe is an amalgam of earth, water, fire, air, etc., it is also transitory. But the spirit soul (which, incidently, has never been duplicated in the laboratory despite repeated efforts) is imperishable, as is its natural, eternal home—the kingdom of God. The process that takes the eternal soul to his eternal home is called sanātana-dharma, or "the eternal religion."
Empirical, atheistic philosophers like Kapila spent innumerable tedious hours researching the material phenomena of this cosmic creation. Yet it remained beyond the grasp of their limited intelligence to understand that there exists a realm transcendental and far superior to this manifested material world. Finally, when their probing minds failed to sight land in an ocean of speculation, they concluded that the absolute truth is unmanifest.