In the verses of the Bhagavad Gita, terms that have modern, mundane meanings may represent elaborate and often complex spiritual concepts. Two of the most important of these concepts as expressed by Krishna are the “world” and “Nature.” In addition to their normal connotations, these terms are also representative of separate complex ideas that relate to many of the other concepts expressed in the Gita.
The “world,” for instance, of course refers to the physical environment, but it more specifically means the environment as it exists as an opportunity and a tool for the spiritual development of followers of Krishna. A particular aspect of the world is “Nature,” another important term in the verse. Nature represents the three qualities of being, unmanifested. These three qualities are ‘sattway, rajas, and tamas.’ It is when these three qualities are in total equilibrium that they remain in their unmanifest state in nature. When they exist slightly out of balance, it is said that they manifest. This manifestation is seen in the caste system. A person’s place in the world, and the “actions of priests, warriors, // commoners, and servants // are apportioned by qualities // born of their intrinsic being.”
It is also a law of existence, that “there are no beings on earth // or among the gods in heaven // free from the triad of qualities // that are born of nature.” Thus, all manifestations of nature (men) are representative of some amount of all three of these qualities in different proportions.
An after thought: in a very rough sense sattway (or passion) might be thought to represent our 'desire' or 'willpower.' Rajas (or lucidity) represents the tempering reason, that both restricts and guides our passions.* Finally tamas is our base physical nature, what keeps us from floating away, so to speak. It is our appetite (in all its kinds).
*See also: Plato, Socrates, or the Phaedrus.