Krishna calls the body "a field," and says it is made up of the five senses, as well as the organs of action, the mind, and the "undifferentiated energy from which all these evolved." It is within the body that one finds the source of desire, aversion, pleasure, pain, intelligence, and will. But the truly free understand this "field," and find the separation between the body and soul.
Indeed, being slavishly tuned to the body's needs only produces imprisonment. Those who find yoga are devoted not to the body, but "to their spiritual teacher," filled with inner-strength and control, since they are detached completely from sense objects. Freedom from the body also means freedom from the vagaries of birth, suffering, old age, disease and death.
Prakriti is the matter which makes up the field, while purusha is the formless thread of the soul's energy. Together these two weave to make the quilt of life, with "prakriti the agent, cause and effect of every action," and "purusha that seems to experience pleasure and pain." Prakriti also bears out the gunas of tamas, raajas and saatvas, and a person's response to these gunas ensures whether they will be tied to good or evil.
Krishna uses the word 'Self' to distinguish that soul which is independent from the body and bears out the karma of many lifetimes. Where the body is simply a function of prakriti, absorbing the remnants of karma of the self for the next round of the samsaric cycle, the supreme 'Self' is without a beginning, undifferentiated, deathless. It cannot be tainted, unlike the body. It might be veiled in maya, but never permanently tainted.
Krishna provides a clearer description of the three gunas. Saatva is pure, luminous energy, free from sorrow, which helps us find happiness and wisdom. Rajas is passion, but guides us towards anger, selfish desire, and attachment. Compulsions arise strictly from rajas. And tamas, born of ignorance, leads creatures towards carelessness, laziness, and sleep.
The Supreme Self, according to Krishna is like an "immutable ashvattha tree," with its roots binding us to the action of the world, and the limbs nourished by the gunas. The truly wise are not bound to the form of this tree -- they do not simply enjoy sense objects and lose touch with the cosmic organization of their body and soul -- in short, where they came from. There are two orders of being in the world -- the "perishable, separate creature and the changeless spirit." The truly wise see that there is a sphere beyond this -- "the supreme Self," who enters the cosmos and "supports it from within."
Krishna makes a clear distinction between the body and the soul -- with the body known as the 'field,' and the soul a product of the greater Self, which allows people to see the roots of their karmic, cosmic cycle of rebirth and death into a physical form. The body is made up simply of senses and sense organs and action organs, but it is a product -- a derivative of the grander Self. As a result, then, if one is slavishly attuned to the bodies' senses and attractions and aversions -- and trusts the body as if it is God -- then one can only live in delusion. The truly wise see that the body is simply a product of a larger, more powerful energy.
Depending on which guna dominates, a person will have different challenges. A saatvic person will have the light of wisdom running through their body, but will have to use meditation and yogic action to move even further into communion with God -- he will not find true peace until he finds ultimate enlightenment. A rajas person, meanwhile, will be dominated by action -- not unlike a chicken with its head cut off -- running to and fro, looking for satisfaction in the material, in the ego, in anything which might satiate all the hunger and greed. A tamas person, meanwhile, has literally just pulled the plug from the socket -- they see no reason to go beneath the surface of things, and live in 'darkness,' dominated by sloth and confusion, and easy obsessions.
The truly wise, however, says Krishna are unmoved by the peace of sattva, the activity of raja, and the delusion of tamas - they do not observe themselves with an eye towards the end result. In fact they are so conscious of the gunas that they can find a true impartiality -- completely undisturbed by whatever comes and goes in their body's temporary feelings.
Krishna repeatedly comes back to the idea of the grand Self or Brahman -- the eternal lord which is beyond all things immediately spiritual or physical. It is a power we will never know -- the source of everything -- and thus instead of looking for proof of it, we must simply focus our minds on it until we can achieve vijnana, or the ability to live in the center of this power.
It is, of course, interesting that Krishna revealed himself to Arjuna before he discusses this grand power, so that we know the physical form that this grand manifestation takes. There is a slight contradiction then between his reiteration that this power can only be unknown because of its magnitude and scope and the fact that he not only appeared to Arjuna, but Arjuna could put it into words. But this tension between proof of the divine's power and a demand for faith in the unknown is at the core of every spiritual philosophy.